Forums without a central focus point--like, say, a general gaming forum or something, where there's a new release of some sort every week--tend to devolve slowly into clubby little corners of the Internet where a small group of dedicated people keep coming back to share inside jokes and be clever at each other. What new people do register at this late stage have a tough time getting into the game, as we've all "known" each other for years at this point.
I hope that doesn't sound bitter or grumpy, it's just the life cycle of these things. The first few months are a fun, crackling, intense time where we're all feeling each other out and talking about everything under the sun. We're in the second phase, where we all know each other well enough that it's like a local hangout..
Would you call me cynical if I said you could apply this metaphor to any relationship in life, either romantic or friendships?
It's a good point though and one I've seen happen on many other forums, once there's a select group of die hard users and discussion dies down, usually the original point is lost a little and it just becomes a "club house" like you said. I say this as a previous lurker who joined late in the game.
Still, I think spoilery discussions about Looper
now the film is out will revitalise things a bit.
Personally, the site still has pride of place in my bookmarks bar in the "Networks" drop down menu with Facebook and Twitter.