The way missiles can miss and come back around for annuva go gave me an idea.
They really shouldn't. A missile could theoretically turn around and come back, but if we assume that both passes are made at the same velocity, and the target is stationary (both might be incorrect, but not enough to invalidate the argument) then you only spent 1/3rd of your delta-V on the first pass. That is not a good idea. Spend something like 90%, saving the rest for maneuvering.
Edit:
Actually, this could happen if you're firing the missiles at very short range. Given that surprise combat is unlikely, so is this case, but it could happen. I'd recommend nukes, though.
And speaking of missiles, Steve, can you add a self-destruct switch for stages? It's sort of annoying to have to manually clean up mines that have launched their payload.