Yeah, the balance issue really doesn't matter to me. If they wish for something crazy, the consequences are handled narratively, and the players know that going in. "All magic comes with a price".
I will say, I'm not a monkey's paw DM. If the players think of something cool and creative that totally fubars my adventure? more power to them.
Unless of course they're dealing with something like an efreet, a greater demon, etc. Thinking that type of entity will play fair? Well, you get what you get.