I touched on this before, briefly, in Matt's Moderator Pro Tempore announcement...
This is a great site, but it's... got no middle class. There are only a tiny handful of users with more than 2K reputation points on the site! That's bad news for a healthy community: most of the tools for editing, closing, review are out of reach for most folk.
You have a few high-rep users, and some moderators, and a huge mass of low-rep users... But there's no middle class, no healthy population of shopkeepers minding their tags.
Obviously, y'all need to be voting - early and often. But I don't think that's the only or even the best solution... At some point, we need to get more users coming back regularly, feeding back into the site.
I see Sam has a "promotional" thread going here - that's a good start. If you haven't already chimed in there, please do so! Anything we can do to help you guys reach more people is a good start...
But beyond that, as an active user of the site, what have you observed standing in the way of users reaching that middle rung?