I don't think it's at all a question or quantity as it is one of quality.

If you have 500 sponsors that are all producing, then well done and keep workin' it!

If you have a buncha sponsors, many of whom aren't producing however, then try out some more programs. Sign up for more sponsors. Throw new ones up in place of non-producing ones. Get rid of the programs that aren't doing you any good and obviously don't seem to work with your traffic.

I can't even count all the programs I've signed up for and, like Michael (dzinerbear), am constantly flooded with requests to join programs, check out sites and movies and ad consoles and links and galleries and so on so forth. Unfortunately, I just can't get around to putting them all up. Unfortunately as well, some I do give a whirl just don't work out for my sites. Some I know just won't do well from the get go, so I never get around to signing up for them.

But if I had the time and the confidence a new sponsor would convert and earn well, I'd be puttin new ones up everyday.