Ah, I forgot about turrets firing through Portals (by default).
That could be a huge advantage if wisps cannot see through portals. Just put a Turret somewhere with a portal in front of it and fire portals around the room. You can fire portals everywhere, floor, walls, ceiling, etc.
I think we just found the best (if not overpowered) solution to this problem. Only reason it isn't OP is because it's way too easy to grief via the Thaumcraft Flux game mechanic.
He should really just make the Flux increase if you're actually making something. Right now you can pretty much quick run by someone's house, place some flaming netherrack, set up a cauldron, and dump 5 or 6 stacks of cobblestone into it, and shift+click. Voila, instant grief.
Still better than the Taint system though.