Vasari have no dedicated anti-structure cruiser. In practice, a big swarm of bombers gets the job done just as well, plus they're useful in combat against the enemy fleet. You can also build and upgrade your own starbase in their own well (as Volt mentions, the Orkulus is itself an anti-starbase weapon). As well, if the starbase doesn't have too many hit point upgrades, the "nano disassemblers" ability of the Jerrasul Evacuator can actually kill it if used repeatedly
