Here's a quick take on something that may be at least part of your problem. The impression I get from your tour is that this is basically a site for people who want an insiders guide on Tijuana whores. Since I and most of the world will probably never go to Tijuana, and even if I did I'm not sure if I'd want a whore, I would have zero interest in joining your site. That gives you a very narrow target audience, especially when most porn surfers are specifically looking for porn to whack off to.
If I were you I'd sign up for an affiliate program and promote a paysite as well. "Just Want Some Top Notch Mexican Porn? Click Here!"
Guerilla Traffic (Their service and support is awesome) has a site called Border Whores that's almost the other side of the coin on what you're already promoting. I can't speak for the whole world but GT is converting better for me than any other program. Border Whores is targeted so closely to the niche you're already promoting that I don't think you'd have any problem converting some of those surfers that aren't making it to the join page. Let's face it, most porn surfers are pornmongers not whoremongers.
Just my 2 cents.