It depends on how early the kostura is obtained...most players get them to jump their planet eating fleet, and so by the time they have them they also have a fleet that can deal with a SB easily...however, I have seen good eco players spam them and focus fire on one planet at a time to wipe structures, not using them for fleet jumping until later...in that case you are betting off fleeting up since an SB isn't going to do you any good....either way, SBs probably aren't going to accomplish much....
If VL are jumping to your planet, they are almost certainly bringing their titan and their caps...and most likely they are also bringing bombers en masse...if you aren't within 3 jumps of your HW, odds are the SB will be destroyed before you get there (and 3 jumps is really pushing it)....once it is destroyed, the planet will be colonized and then stripped....the key is preventing them from being able to colonize, and only culture can accomplish that...
Flak and repair bays aren't likely going to do too much (maybe like 200+ flak would but that isn't something you get in a pinch)...the titan can move right in and hit structures as well as any flak you have, so that's basically feeding the titan even more and not really stopping anything...
Bomber spam can be dealt with by fleets to a degree...mass fighters (maybe with flak) and cap abilities can actually do well...you may lose a cap or two, or you may lose your titan, but once the bombers are gone they lose their firepower and you just mop them up with LRFs or LFs or Snipe or whatever...so, the bombers that can wipe SBs really fast are not necessarily instant kills to well-made fleets...
The typical VL planet eating fleet is a titan, 4-6 caps, and lots and lots of bombers...obviously you have 1 or 2 jarassuls for colonizing (and maybe drain planet), and the other caps are personaly preference...the thing is that the VL fleet doesn't need to be well balanced because it can just keep running away....
Even if you are 2 jumps from your HW, the VL fleet can easily escape (they'll bomb out PJI's no problem)...it's only if you are 1 jump (or 2 jumps that can be done really fast) where you stand a chance of catching them, and your fleet really is the only thing that can do much against their planet eating "foray"...if you are close by, RB wiping out their bombers may still be useful, and wailing may also be a possibility if you think you can wipe the carriers (you'd have to have a nearby desert or terran to even stand a chance, though)....so basically, building an SB to deal with VL might buy you some time, but likely not enough to make a difference...
In my experience, trying to stop a VL planet eating fleet is pretty much a lost cause unless your fleet is close by...your only option really is to have culture everywhere so they can't colonize planets they bomb out while you go and take the other team's planets...and if you can't make headway on the frontline then you are hosed, because if you try to come all the way back to your HW, they'll just leave and now you wasted a bunch of time doing nothing but phase jump...
