I had this experience early on (1998 around) when I accidentally stumbled on a rich client who was very religious and introduced us to his church where almost all men were rich business guys (only ceo's, investors and their families etc). It was a great niche money wise, but as my co-founders and myself were (and are) atheists, we really couldn't work with them as they continuesly mixed religion with business and we cut ties after a few projects.

But it is a good idea I think if you can get into a large (enough) group of a certain demographic that doesn't bite (too much?) with your own beliefs and values.