I have a site that is getting a good 1.2 million page views/month, about 13k uniques a day. I would share 33% of Adsense income for a full year to the person that believes they can increase revenue past a very low income threshold (I can't mention the amount here, but trust me, it's a low number right now). Any takers can shoot me an email and we can discuss further. The site is webguitartabs dot com. Hell, if you just want to give me some pointers, that's fine too for the sake of discussion, but if someone is interested in a serious opportunity, I'm game... and I have other sites as well.
With that kind of traffic, why don't you create some member's area that will have some special stuff that you will not have in the free area? Most members will stay for three/four months but still it is better than AdSense. It is an old model that porn sites adopted way back in 1996. Get lets of free traffic to a free site and than offer something extra on the member site.