Kostura does the following things: Damages every ship and structure in orbit of the planet hit, disables them for a set time and lastly, opens a temporary phase lane for a fleet to use at any phase gate.
That explains a lot. In a recent game I couldn't figure out how my ships were able to skip halfway across the galaxy to the targeted planet.
This is what I've noticed: 2 or 3 shots from some Novaliths are usually enough to wipe out an enemy coloney, whereas 4-7 shots from some Kosturas are enough to remove all ships/defence platforms around a coloney (not including SBs, or occasionally a tradeport/refinery). I like timing my Kostura's to fire right before my fleet arrives, so all enemy defenses are gone (or at least disabled) when I come out of phase space.
The Kostura is actually one of the main reasons the Vasari are my favorite. I find it more usefull strategically than the Novaliths (though the Novaliths are still great fun).
If I only build 1 superweapon this year it'll be the deliverance engine. Why?
A. I play the Advent the most as they have maximum cool points
B. If I can build several superweapons (like multiple kostura's) I probably don't need the superweapons to win.
C. In a serious situation (match is undecided), there is a rare chance i'll get to build a superweapon, but probably just 1, b4 the odds tip or I need to rebuild my fleet.
D. IMHO if you only have 1 superweapon, the Deliverance engine does the most for you. A deliverance shot will scout the planet you are about to attack (combined with vision of the faithful) It will then proceed to grant your fleet their culture bonus deny the enemy their culture bonus AND give your fleet a generic combat bonus in the upcoming battle. Suddenly combat odds are very much stacked in your favour. And as a side benefit it'll drop someones allegiance and lower resource extraction rates for a while.
This compares with: 1 Novalith Oh noes some people died! I guess the TEC will lose credit income for a bit... like it mattered...
1 Kostura, the jump gate is cool, as is the long building stun (screw you repair bay) I think however that the damage done by 1 kostura shot is less than the benefit gained from being hit by the deliverance engine. Especially as the kostura does bugger all to starbases... with the deliverance i get all my buffs making star bases go down MUCH more easily.
Anyhow yeah, don't play Vasari: Join the Unity!