I think it's a really interesting problem potentially because of people like me. I've been lurking here for a very long time, actively checking other people's mods out, learning the editor, working with my mod team, and not posting. Like there might be this silent extra 30% of the community who simply aren't noticed because they aren't participants.
I think if we could figure out more ways to lure out the lurkers and get them to start participating, the forums would begin to feel busier, and the community more alive.
It could be however, that no matter what sized community you have you will always have a silent 30-40%. I'm really just speculating based on what I've seen. If you look at viewcounts on some of the posts on the forums they almost feel overstated. It's like there's absolutely no way that there are that many people in here. Like I said though, there's probably a significant number of people just watching while they work away on their own mod, and if we can get them to share their ideas we might all benefit.