I know quite a few people from my time in CAP. One of them an active board member here even!
Both of us I know joined in under the cadet program, and went pretty far in what is basically the military style leadership training in the program. As well, when I was 18-21 years old or so, I began spending a lot of time working on search missions. Either sitting around mission base, keeping track of a dozen planes and a few vehicles out on a search that I can be certain some of the ol' retired age guys could not have handled with about 20 sticky notes on each of them. Move on to flight roles, and into ground searches. All this was great fun, and gives that feeling of something done. Especially when a ground search results in finding a downed plane (though that pilot didn't survive).
I never got into doing the flying, as there is a ton of paperwork. All fairly mundane stuff though, and if you want to do that stuff, it would be fairly easy to get a bunch of pre-printed forms set up for yourself, and do some fill in the blank stuff.
I think CAP is useful for what you can do, but it is only what you make of the program. Avoid those few (and there really are very few of them, though vocal) that are on some sort of power trip, and it becomes a good thing.
Some of the things CAP gave me, before the age of 20:
A paid 2 week trip to Europe, and Washington DC, with friends.
Professional leadership training.
Awareness of fllight safety, by seeing what was hard or easy to find on a search.
That last thing keeping in mine always what to do in my flying days now.
A number of friends and contacts with similar interst, which resulted in a lot of free flyin' trips.
An understanding that those who tend to hate CAP base that on some very specific limited negative experiences from those few bad apples in the organization.
Flights in simulators, C-130s, miltary helicopters here and in the UK, and more, all of which would be nearly impossible for your average joe civilian on the street.
All in all, I think I got a good deal. Put maybe $500 into it up to that age, and a few hours a week of my time.
I do stress that CAP is not in itself a flying club. Their 3 missions: Aerospace Education, Emergency Services, Cadet Program, can all allow some flying, but the flight time will be a result of supporting one of those missions.
Oh, it also has little benifits of allow access to military flying clubs. Locally, the navy club has a t-34 members can access, if you are into that kinda stuff. I found it fun back when the T-34 was $34 an hour wet, which was a few $$ cheaper than a 172 at the time.
Josh