I wouldn't be too concerned that most members don't actually post. I used to run a large 'fan' forum related to Buffy The Vampire Slayer (shaddup!

) and the people who frequented it were madly passionate about it. I mean
passionate! And yet, the vast majority of members only ever lurked. No idea why, but it seems to be the norm on all kinds of forums.
Interestingly, once they actually posted a couple of times they usually stuck around.
This type of forum is a little different and you probably will get a large group who just want to post their links and bugger off. Pity because they miss out on the whole networking thing.
But yeah, the majority are only ever gonna be lurkers. It's the way of it I guess.