Except not really. Mines have an activation time, which means in the worst case you can send a few suicide scouts in to clear a hole for your jumping fleet.

Since the Vasari base moves, the invading fleet can build it at the edge of the grav well. That means to stop it, the defender would have to move away from their own tactical structures. At the same time, the Vasari are best suited to take out starbases without anti-structure cruisers, with Nano-Disassembler and phase missiles/subverters. Furthermore, the starbase is painfully slow, giving your bombers a lot of lead-in time to get its shields down.

Also, the attacker has the Kotsura.

Kostura is not quite a viable argument here. You can have a well upgraded starbase in, like 30 minutes? While Kostura requires craploads of money spent on 8 weapons labs, expensive research and loltardedly expensive cannon itself.
You have to sacrifice your whole economy if you want to rush to kostura. It's not something you can dish out of your lunchbox at any time. On the other hand, a starbase with 2/2 colony pods becomes one neat money machine.

So I'd stay away from Kostura for the sake of the argument. Torpedo cruisers and the starbase itself can be fielded earlier and with far less sacrifice in your economical sector. I agree that once you have a kostura, every enemy planet is one step from being conquered. The problem - kostura won't solve all the issues. You still need a force to take and *hold* the planet you're assaulting and a force to defend your own ass in the meantime.

As for annatar's ideas, every single one of them may be used by the defender as well as the attacker. Particularly the bombers aren't such an easy bet now with the phasic trap working for the defender. Basically you have to keep your bombers in the docks until the defending starbase is right at your doorstep, because otherwise the defender's phasic traps will have them locked until the end of battle.
Space Whale, subverters and phase missiles are as much of an advantage for the attacker as they are for the defender, because any of those tricks may be used with just as much success on the attacker's force as they can be used on the defender.

The only real advantage the attacker has above the defender is the Kostura - which, unfortunately, is the most endgame weapon one can find. Seriously, if your enemy has a kostura fielded in the first hour of the game, it basically means he has no fleet and that you can simply ride over him with anything.

The range advantage of a long range cruiser is also beaten by a TEC colony ship. That +25% range really helps out a starbase.

I agree with this....the assault cruisers die fast.  The only place I find them a worthwhile investment is in gravwells with very little fighter coverage and against the non moving starbases.  The Orkulus just gobbles them up.  They are great for taking out baby starbases, but then again, your fleet could do that fairly easily too.

The Kostura doesn't do much damage to the starbases, in my experience...even if you fire with many Kostura's...the reason it is so useful is it shuts down all the other static defenses and if you fire enough shots, does significant damage to defending ships.  This gives you a chance to kill the Orkulus.

Haha.  Don't play Vasari?

OK...just for the record, I totally agree with you that Vasari vs Vasari is difficult.  I have other posts in other threads where I mention this is like trench warfare where it is difficult for either side to make progress.  As you mentioned, trying to get your own offensive Orkulus in play while dealing with an enemy fleet, a full grown Orkulus, other static defenses, enemy strikecraft, and probably mines is a massive pain in the ass.

Now, to respond to your comments:

They do a lot of damage, but they also go down pretty fast to fighters...faster than they can be repaired.  I think it would be nice if they had a bit more range....but whatever.....I find that carriers work better for taking down an Orkulus without losing tons of ships, it just takes a long time.

They do not get shut down like static defenses.  They might get briefly stunned, like a ship, but for the most part they shrug offf Kostura strikes.

I don't fully understand what you mean by first thing in the morning and survive 15 minutes.  I don't think anyone said to rush for Kosturas.  They are very effective to take the remaining super fortified worlds after you control most of the map.  When a team starts losing they often have a nasty habit of putting multiple player's starbases in the same system, hiding their remaining fleets there, and waiting for you by their PJI's, static defenses, and mines.  It can be suicidal to directly invade these systems, even with a very powerful fleet.  Kosturas are invaluable to soften up, or even destroy all of the static defenses and defending ships so the starbases can be attacked.  It is an endgame strategy.

I think the moving starbase is a huge advantage. so, if i have to decide between Topedocruiser and moving starbase i will choose the moving starbase everytime. As Vasari against Vasarie its harder, but your opponent has the same Problem. So may the better tactic win...

PS. The reason I wrote this wall of text above is to show you how limitlessly sophisticated it is, for a Vasari set up against an entrenched Vasari, to mount an effective offensive.
By effective I mean an attack, during which the attacker has at least one advantage above the defender.
In Any other matchup the attacker has an advantage.
- in Tec/Adv VS. any faction , the attacker has the advantage of torpedo cruisers, simply because they are a threat to the defender and the defender has no use for them. Vs Vasari it is harder, but the torpedo cruisers CAN shrink the Orkulus' hit point count VERY fast. Just give them good cover and you WILL cause trouble.
- in Vasari vs. TEC/Adv , the Vasari have the advantage of moving starbase. They have to set it up out of the Tec/Adv's SB's reach, keep it safe until they are ready and move in.
Lastly, in Vasari vs. Vasari matchup, the attacker has only the Kostura (which is foultardedly pricey to set up) and it only eliminates the tactical structures, which the attacker can't bring with him anyway. So neither side has tactical structures... excluding that, both sides have exactly the same aces in their sleeve, except for the defender having a well developed starbase which pushes the odds heavily in his favour.

There must be a deeper story behind what you said. Listen to yourself - I played two people. they had fewer planets than I did. I managed to take three of their inner worlds, along with one's homeworld, with 1/3rd of my fleet. I had so many kosturas that I wiped their world clean of everything but the starbase.
I mean, come on - wth were they doing???? it sounds as if you were playing Easy AIs.

Either
they overslept the first hour of the game OR
they fought 3 other people while you built up strength OR
they made a crippling mistake at one point OR 
you stabbed them in the back while they were fighting in another system OR 
you were desynced and in their game you were dead for the past five hours OR
they were idiots.

I say again - we're not fighting a nib who thinks a starbase in every gravwell will save his ass against everything.
I'm talking about assaulting a person who owns at least as much as you, who knows that time is on his side and who just fortified a good chokepoint to prepare a force that will crush you.
I'm talking about assaulting a good Vasari player, who has a capable fleet, phase stabilizer nodes and a single Starbase defending a choke point. You can do it with TEC, you can do it with Advent, if you're on equal terms. But you need double the funds to do it with Vasari. That's an error.

In Starcraft (in my earlier days as a protoss) I could defend a chokepoint for 1,5 hours against a much better Zerg player with only 3 reavers, 2 shuttles, 6 corsairs and some photon cannons. Anything he threw at me was sent to him in trucks when his swarms caught a reaver scarab. But that game was lost and we both knew that. I could not win when he controlled 85% of the map and I controlled my own base only.
It looks like you fought such a game - an already won game that you just finished off using the fanciest tools you had.

Ok... You want an assault cruiser... What are you going to do with it?

Speaking as an advent player: They really do not help much agains a Vasari SB.

The starbase you are describing 2 offense, 3 defense, + other upgrades... it would shrug off the damage from the cruisers, move towards them, and grind them into powder. The thing that makes assault cruisers so effective against a SB is that the SB cannot fire back. Their range puts them just out of range of a static SB.

Nullify that, and the cruisers are toast.

What you are describing, assaulting a heavily fortified Vasari grav well, it's a problem no matter what race you are.

For that grav well, it comes down to your races superweapon, and a whole lot of ships.

As soon as they started Entrenching to hold me off, they start losing because they can't project power as hard as I can.  I built no starbases that particular game.  It was against another member of DT.  Killing another Entrenched Vasari is a slow painful process of finding the chinks in their armor and slowly expanding your holdings while chipping at their least defended worlds.  It takes forever, I'm with you...there could be some improvements made somewhere.

If two Vasari players have equal expansion, then Entrench heavily, then make so many defenses they have no room for Kosturas, then yes, I'm afraid they will just have to stare at each other across the border.  I'm just trying to give you ideas.  Very few games are complete deadlock....even with Entrenchment.  Someone is usually winning and someone is losing.  The problem with Entrenchment is it takes an extra hour or two when the forces are very equal in power and then Entrench.  It is entirely possible to have a true stalemate...I've just never seen it.  I either eventually win, or if my allies collapse, I lose.

Starcraft?  That was a good game.  I hope Starcraft 2 is as good or better.

People who focus more on building defenses early seldom are able control as much of the map.  Entrenching is valuable if you have allies winning their fights that will come rescue you, or if your opponent actually suicides on your defenses.  Otherwise, the player who can project power ends up with a bigger empire and has the resources to employ superweapons to crack the last defenses of the Entrenched player.  This pattern repeats itself over and over.  If this wasn't the case, no one would be able to win a game of Sins because you would only have to build defenses not to lose and there would be no incentive to attack. 

Defenses are more cost effective in the gravwell where they are built, but they can't be everywhere so the guy with the fleet has his choice of your undefended worlds.  Obviously player skill comes into play as well and Entrenching a critical chokepoint might actually be the wisest choice in some situations -- but usually it is better to just build light defenses and park a small fleet there so you still have the option to attack.

In the cases where I obliterated the enemy gravwells, I was certainly bigger, because the Entrenched player spent early resources on defenses while I spent mine on fleet.  My fleet was sufficient to take additional undefended worlds and assist allies in wiping out other players, allowing me to continue growing.  In the example where I jumped past a double chokepoint, I whittled the player down to two worlds.  I don't usually have to build more Kosturas because most people are decent enough to quit at this point because they know they can't win.  I also have been playing TEC a lot, because it is a lot easier to just Novalith people who turtle up than it is to use a Kostura and then have to go siege the world.

Based on your assumptions, your conclusions are perfectly sound for two players who have spent all their time defending their worlds before they decide to kill each other.  If they have expanded equally, both entrenched fairly equally, then yes, they will both find themselves at an impasse.  In practice, my games never turn out this way....I'm assuming yours do, and that probably reflects a playstyle difference.

The main problem I have with the Assault Cruisers is they get slaughtered by strikecraft.  People often tend to have many carriers end game and large numbers of strikecraft can kill an Assault Cruiser in one pass, even if you have repair, etc.  The Orkulus by itself is not a big deal, it is when they are heavily supported.  As you say, it takes about X3 the effort to assault a world as it does to defend it, which would certainly be a problem if both players had exactly the same capabilities because they both played sincity equally for an hour.

I think all the races need stronger options for taking on heavy defenses.  I'm on vacation from the game for a while, and hopefully some new stuff will be in place when I get back.  Entrenchment games have a lot of new strategies, but some of them are way too long to be practical.

Back when I learned what the first expansion would be, I was afraid it would make the games longer, and it has.  I hope the next expansion offers some new alternatives.

I completely acknowledge that the Kostura, and all the Super Weapons, are great for finishing off people who are smaller than you but are heavily dug in.  That said, the Kostura is a tremendously powerful tactical and strategic weapon.  It can make the difference in what would otherwise be a close fight and it more than pays for itself in these situations.  Chances are the other player is as reluctant to attack as you are by this stage of the game.  If you can maintain enough defense that the other guy can't break through and you get Kosturas up and running, you now have the ability to inflict damage on the other player completely from the security of your defenses at no loss to yourself.  Kosturas also don't filly fleet capacity, the guy with the bigger fleet is at a higher fleet supply which means his economy is smaller unless his empire is actually bigger than yours.

Even in your scenario, you state that it is three times more costly to attack, but the guy who didn't build Kosturas is only at two times fleet size.  If two times the fleet size isn't enough to attack, maybe your own math supports using Kosturas from behind your defenses?