Now looking at this after I finished its a long read but probably useful , hopefully it doesn't get to boring. (and if Ironclad uses this I expect some credit, haha)

Well I'm going to add my two cents into this battle royal. Remember that I have not yet played the new micro-expansion, but I will get it once it is out.

Personally I see the starbases as something that should be able to stop a enemy fleet from jumping to the next system or thinking twice of attacking the system that the SB is inside of. As such what the SB should do a ) stop the fleet from jumping through/to the system b ) cause s*** load of damage to anyone who does go to the system it is in c ) make it really hard to avoid if you do decide to go through the system

Defensive SB

The starbase to do this would have to have huge range. Now I am talking the whole gravity well of the planet it is defending (now remember it has to be defending one of your planets). Which would make this a force to be reconed with. Also any fleet that does wish to skip that system would have heavy losses. Unless they decide to move around the whole systems gravity well, at which point they could take loses from fighters, or the player attacking. This would accomplish the fact that anyone avoid it would still get some damage done to them, and would have a long journey around the system.

Now if you are asking how it can attack the whole system, we could contribute this to the system being used by the player and as such they know were anything such as debris, astroids, comets, etc are within the system and this would attribute to the great range of the SB. (I would also take the assumption that for systems with planets that are colonizable you can build a SB only above the planet, since it will be defending)

And of course the location of the SB would have to be on top of the planet (either North or South pole) since this would be the only location allowing it to attack any direction without going through the planet. And by on top I mean that it wouldl be floating in space not littraly on the surface of the planet.

Tactical (offencive) SB

Now as a tactical base when you are attacking we would decrese the SB, range. This would mean that if the SB is made in enemy territory, or an uncolonizable system it would no longer have the advantage of gravity well radius, instead it would be limited to about a 1/2 to 1/3 of the diamiter (careful here the SB in a home system would have a full radius or diamiter range same thing, but once neutral or enemy territory it will be limited to 1/2 to 1/3 diamiter, 1/2 diamiter is equal to full radius unless i screwed up my math terms). This would limit its destructive capabilites from being over powering where it can take a system it self, though it will help imensly. If used against an enemy system, it would not convert to a defencive SB, you would have to scuttle or dismantle and rebuild it, since it wouldn't be build over the top of the planet in that system.

So the question will be asked then what is the point of a defensive SB, well as you can see it has the advantage of creating a cliff wall against someone attacking the rest of your systems beyond it and the system its defending. Sure they can but it will cost them time and reasources. Also if you use a tactical SB and capture a system. It would be in your best interest to dismantel/scuttle it and build a new one over the planet as a defencive SB or to be able to build another one later on.

Now a little about movement of the SB since I have seen a few people talking about it. Now I think thats just dumb. Don't get me wrong but a moving starbase would be wrong, especially when people will be using it as a tactical structure.

Cost

Now this should have two different structures costs associeted with it.

a ) D-SB

Super high costs with super long build times. I'm talking about 10-15min build time with enough resources to rebuild a 250 lg strike force. So something along the lines of 8,000-16,000 metal and crystal and at least 40,000 crd. Since its meant to stay you would really feal the pain of getting one of these but you know its worth it once it takes on a entire fleet by itself.

b ) T-SB

high costs with faster(now it'll still be long). Now were talking a faster cheaper build since this is not used as something that is meant to be pernamnet. Instead it will be designed that if I am attacking a system I need the power now, not later.  So something around 3-5 min build time along with a cost 3,000-7,000 M/C and about 30,000 crd.(hey remember your still part of an economy those workers won't build it for free, they need danger pay, just to keep it going with the story)

Strengths

Well what will you be getting with all of this expendature.

a ) D-SB

High hit points, I can't stress this enough since this is meant as a pernament instilation it should have more hit points. I don't care if you have 13 missle cruisers(I'm looking at you Exterm123), I want you to leave this fight after winning or loosing feeling like someone kicked you in between the legs(and in the case you lost they just never stopped kicking)

Range, I have already mention what should be done with the range.

Attack power, simply put this ain't your daddys m-16. This sould be along the range of getting attacked by 4-6 fully upgraded Kol battleships. Also it should have multiple targetting systems. So I'm not attacking only one ship with more force then is needed.

b ) T-SB

Low hit points. Now since we are attacking and this is meant simply to give you a extra advantage, it shouldn't be able to survive a lot. It was built fast and cheap so thats how it will work, fast and cheap. This should maybe have 20,000 hit points so that its not to hard to take out, but still a challenge.

Range, like I said already decent range. Something that will cover a lot of ground but won't be the king of the battle field. You should be able to place it and if you are good enough to drag an enemy into its range it will hurt them.

Attack power, Now since its primary use is to set up a beachfront it should have about 1/2-3/4 of the attack power of the D-SB since its just meant as a temporary fixture.

Right now I feel my case of Rockstar running out, so my ideas are running short. SO I'll just post this, I hope a decent conversation will be started because of this. If anything I'll add later.

PS I know there are mistakes but give me a break its 15 to 5am.