Personally, I don't see the registration requirement as a big hurdle. However, note that two of the more popular SXM forums allow anonymous posts (TTOL and GoBeach). One with and one without captcha.
I'm a regular contributor to both forums, and DineSXM is a sponsor of TTOL.
They also have multiple moderators who delete spam on sight, maybe this is something you could look at?
If you do not want to go that route, you might have to start "bribing" visitors into registering... Make the ads disappear for registered users, implement a community driven kudos or bonus system for answering questions and posting quality content... Or you could look into an OpenID type of solution, but I doubt that your audience would have pre-existing id's. Also, you'd have to relinquish control over your registration data.
On a tangent: to be honest, I'm a bit put off by the sheer volume of advertising on your site. It cheapens the experience and distracts from the quality of your information. It probably has a negative effect on your readership, and may also adversely impact registration levels.
More related to the original topic, a site we launched in early 2008 - DineSXM.com
- requires registration to access some advanced features; I notice the same type of hesitation when it comes to visitors' willingness to register on our St. Martin / St. Maarten dining guide. I'd be very interested in finding out how you plan to tackle this issue, a similar solution might work for us too...
Norbert - DineSXM
<b>DineSXM</b> - <a href="http://www.dinesxm.com/?utm_source=CONL&utm_medium=link&utm_content=sig&utm_campaign=DC1">St. Martin / St. Maarten Restaurant Reservations & Dining Guide</a>