Another pokemon that I think ought to make a decent user of this item is regular form Blastoise. It can still perform a utility role while holding an Assault Vest as most of its utility moves happen to be attacking moves anyway. It can run Scald, Rapid Spin and Dragon Tail, all of which are damaging moves, so Assault Vest's downside doesn't come into play. The fourth move is a little more difficult to decide on, but the frontrunners are probably Ice Beam (to nail the dragons and grass types that will switch in on you) and Dark Pulse (With Foresight out of the picture, Blastoise can use this to take on any spinblockers that pop up in front of it.)
It'll miss its leftovers and hence greatly appreciate Wish support, but in return you get an extremely potent sp. def sponge, seeing as how you could spec out Blastoise in such a way that it was extremely specially bulky already.
Of course, whether it's worthwhile using over Mega Blastoise is another matter entirely.