It's tough. Unless you want to place a new starbase in every single planet's well, the Vasari have to use a lot of little tools that all add up against a starbase, instead of the single designated anti-starbase tool of the other races. The nice part is that many of our ships have offensive abilities that are good against a single target (the subverter, or the Skirmisher's researched Interference ability, or the Kortul's Disruptive Strikes passive), especially if that target depends on activated abilities like a deflector shield or meteors or something. And, the Vulkoras' Assault Specialization passive gives a big boost to its own phase missiles against structures; since the Vulkoras is mostly armed with phase missiles, and they all face forward... bottom line, a group of Vasari capships can do some impressive damage to a starbase. It's not the no-risk standoff kill of a torpedo cruiser or a massive strikecraft swarm, but it's still good enough to keep you from bogging down too much. Two or three capships with minimal support can take out an unupgraded starbase with ease; in the late game, I'll have 4 fleets of 4 capships (each with 10-15 transporters, 5-10 enforcers, some flaks, some subverters, some overseers), and each of those can take out a heavily-upgraded starbase with little effort.
The plus side to this is that there's no obvious target for an enemy starbase to go after first; Orgovs are helpless against a concerted attack, and smart players can micromanage their strikecraft to kill those first, but there's no easy target in a Vasari fleet the enemy can target to make his starbase "safe". At best, he can try to destroy a colony ship that you bring in, but since you can build the starbase immediately after jumping in, there's little risk there. And with the brand-new "assault deployment" tech, Vasari build their starbases in enemy wells much faster than before.
