Decided "reality" shows fall into four categories. In no particular order:
1. Those that can be truly called reality - Cops. Granted there is editing for time and entertainment, but what you see is unscripted life unfolding. Continuing with Cops as an example, you probably do not want to be "cast" unless you're law enforcement or go to jail on national TV is on your bucket list.
2. Those that are supposedly peeking into the regulars actually lives - The Real Desperate Housewives of... These have regulars that continue from season to season. The purpose of being on a show like this is marketing. The only thing to win is opportunities that come up because you are now a recognizable face/name.
3. Contests to win a prize - Survivor. The purpose of being on this type of reality show is to walk away with the big cash prize. The goal is to stab all other contestants in the back (proverbially speaking) and have them proclaim you one of the greatest people they know and that you deserve the big prize.
4. Contests to win a contract - American Idol. While winning the contract would be cool, the purpose is to get noticed by the powers that be by showcasing your talent. Guess that would be a recording studio for American Idol contestants. (Don't know how singing careers work.)