Hey Panman,
I joined AMRA their first year and the several claims around the Coulterville area I prospected produced some good gold, fast forward 3 years and I am sure the claims have been hit hard but probably still have some good gold if you poke around enough, they are in the thick of gold country. I know they have claims all over other parts of Cali but I have no idea of their potential. There is good and bad with joining a club, the good is there are a lot of fun areas to go prospect without having to worry about being on someone else's claim. The bad part is the claims have been hit and if you get a good hole going, you have to finish it or someone else will do it for you. There is the socializing thing as well, wasn't sure as to put it in the advantage or disadvantage category. If you're a beginner or just like to socialize, this is an advantage, if you're not a beginner and like to prospect alone, like myself, then this would be a disadvantage.
Spiller