Not at all, I think it's a fabulous idea. Just be sincere, don't gush -- "Thanks so much for having me over, I had a great time with [X thing your really enjoyed" and I think they'll love it.
I'm in a similar situation -- my family can be pretty trying. So when someone else includes me in their kind, functional family, it means a lot. I've never had a negative response to a sincere thanks.