Good looking site (good design) is a big plus for any site on the net. Doesn't matter if the site is of amateurs or pissing niches....
Every product or service should look (or be served) the best as possible. Even toilet paper sells better when it's colorful and well packed.
Don't think web site designers force you to buy designs when you can go copy other site's look or make a few links yourself and call it a paysite.
The best thing for paysite is when it's well designed and loads fast even for 56k wankers, so the best thing would be white background and blue link on center telling "JOIN NOW" (c:P
Cheers