Wow... This post is me about 6 months ago.
One thing no one mentioned yet: tells. Players that are "just having fun" have so many tells it's unbelievable. Watch their hands, watch what they look at after they see the flop, watch which color chips they go for first, watch everything. Check out anything by Mike Caro, that stuff is gold in these loose home games.

Btw, in these ultra-amateur games, if the blinds aren't absolutely huge, you might be able to get about an 80% win rate if you can read everyone in the game well, but don't do it. I have been involved in games that fell apart because one or two guys left with the money every week. Let the fish have it every once in a while. If you've won a few weeks straight, play like they do for a little while, pay them off when you know they have a hand. In the long run, it's +EV.