So my wife wanted to take a ballet class because she thought tribal dancing and belly dancing might not be for her, but she wanted to do something active with the Milwaukee Rec Department. She doesn't know what she needs to wear, or if it will be a class filled with a bunch of retired out-of-shape ladies or semi-professional dancers. So, we'll let you know in case your wife ever wants to sign up for the class.
Update: My wife said most of the people in her class (who stayed in the class) were former dancers who really knew what they were doing. The instructor mentioned that many people tended to quit her class, and we surmised it to be because of her fairly high expectations. I'd say take it if you've at least danced before, which means I won't be taking it.
This would seem to be the problem with any adult sports class for a recreation department as you might have old people mixed with young or physically fit mixed with the inept. Kids are grouped by age, and there are still plenty of differences between each individual.