I'm a club member and I learned to fly the "old fashioned way". That is, with .40 sized glow trainer and a fellow club member/instructor standing beside me with the transmitter while I manned the buddy box. It is quite a comfort with a glow power plane to know that you can just quietly say your instructors name when you get in trouble and he can take control and recover the aircraft.
I learned to fly this way because it is what I wanted, I had no interest in electrics at the time. As time has gone on I have become enamored with park flyers too. I usually fly them at my club field as some of the other guys who fly the big glow fuel and gas planes do. I think it's just a nice change of pace. I guess I'm lucky in that my club dues are what to me is a very reasonable 40 dollars a year.
As far as AMA membership, I think that even a strictly park flyer pilot should seriously consider it just for the insurance alone. Even as careful as you guys are, you have to have a "what if" mentality. Even as light and slow as a park flyer may be , it can still cause significant damage if it were to hit a car or a person. You also get a pretty fair magazine for those AMA dues.
The only other thing I would worry about with park flyers is a person who somehow thinks that because they have mastered a 2 or 3 channel electric plane that they can just move right into a .40 glow powered bird with no other help. As far fetched as that sounds I have seen that kind of thinking on more than one occasion.
The hobby is in a great stage right now with park flyers and ARF's, new advances in battery technology and reliable affordable feature rich radio gear. It has something for everyone.
Let's all enjoy,
Michael