Just looking at the stats on the manual, I've no idea why the vamp exists.
Avenger is 50% cheaper, 30% faster and has 2/3 the AA DPS of the Vamp. Not to mention that having a 160 burst damage missile that rarely misses is worth alot as salvoes can prevent that Licho from dropping the nuke or a krow from getting away.
It can also shoot ground! (although it's pretty useless at it)
The only advantage the Vamp has is hp, having 3.75 times more hp than an avenger. So Vamps can distract enemy AA far better than Avengers, especially flak AA. (unless you're trying to suck up the missiles of a screamer, then gnat wins hands down)
Therefore, unless you expect to have to fly over enemy territory chasing aircraft, there's no point building vamps. Avengers are better AA than the vamp.
Another thing is that I often see fighters overtaking their targets (they're faster than bombers and gunships), so much so that they can't really stop their targets at all, only ensure the targets don't get away alive.
There ought to be a widget that slows the fighter down to it's target's speed when it's firing. A trick could be to write a widget that hits wait commands to prevent fighters overtaking targets. (I can't do this, its just hypothetical)
