This kind of thread very rapidly turns into four pages of people who make fun of CAP and people defending. I belonged to both groups at one point so I'll try to give you my objective take.
How about I start off with a one sentence description? CAP is a great group, but unfortunately is full of CAP members.
The good. They serve a valuable purpose that you can be a part of. You do have access to fairly inexpensive airplanes. It's neat being an adult supervising the administration of a program that aims to better youth. It gives you a taste of what the military is like (granted a small taste). And really it can be a lot of fun. They also allow for a higher grade when enlisted in the Air Force if you progress to a certain point in the cadet structure, but that doesn't sound like it would apply to your situation.
The bad. As mentioned above, the people. Some of the biggest tools I have ever met i met through CAP. There tends to be a lot of adults and cadets who tend to take their CAP rank WAY to seriously. A lot of people think of it as a good way to build cheap time, but honestly the process for renting their aircraft is so tedious to the point of not being worth building ANY time. To me it also felt very improper wearing a military uniform.
That's all I can think of off the top of my head. Others, I am sure, will have many more pros and cons. To sum it up, the people are what really turned me off the organization. Miliage obviously varies between squadrons. Go to a few meetings and see what you think. If you don't like it, bail. If you love it go get some reflective aviator sunglasses and jump right in. Never really know till you try.