This is something that we have looked at. We do share some of the content between sites as a bonus but I agree with Lee that it is crazy to give them everything you have on all sites for one price.

I have used this concept when I was working in str8 stuff, like putting an anal, oral, ebony and fat girl site together, and the surfers really seemed to like it. And it makes it easier if you have multiple sites and they get updated once a week.

We have some sites under development that will offer bonus access to some of our other sites, but I do think the niches need to be somewhat complimentary. ie. someone joining a mature site probably wouldnt find a bonus twink site of much value, but pair it with a bear site or something and it's on.