Ehhhh... Vasari don't need any help vs structures.
While they're missing dedicated anti-structure ships, they have all the tools needed to clear defensive structures efficiently.
Subverters can disable structures. They have a strong collection of defense reducing abilities and a highly durable fleet. Their superweapon not only disables and damages all orbital structures but lets you bypass heavily fortified worlds entirely. I really enjoy attacking a beefy starbase with a Vasari fleet and watching all the debuffs dogpile...
Man, I miss playing them, I need to load up some Diplomacy...
*EDIT* And of course you can do all this without taking supply away from your ship-to-ship fleet, because all the ships that have useful anti-structure abilities are good in direct engagements, too!