The fact is, people visit adult sites to fap and are done within a couple minutes. Once they blow their load, it's pretty much it. You can't expect great conversions unless you have a good targeted group of users and most don't want to spend a dime on porn.
It might not be the most ethical way of getting good users, but adult sites are the highest hacked on the net, and being able to obtain these lists of users would increase your profits if used right considering these users have and do spend money for adult content.
As for affiliate programs, not sure what you use but XProfiles.com and CECash.com pay $1.50 per email signup and more for paid members. Large networks like PornPros, BangBros, RK, any other networks using CCBill, and many more generally pay $25-$50 per signup and offer Rev Sharing. WetDollars has made me a bunch of money but they shave HARD, resulting in about 1 in 5-10 signups actually being paid, so I don't recommend them.
Another method some do is uploading content to hosts that pay per so many downloads and give their users the download links. I don't because I'm too lazy to do it, but have heard good success with it.