I think that it's a pretty well known phenomena that most people never make it past the first page of search results in Google (or any other search engine). Likewise, I imagine that once a question falls off the front page in SO, it's relatively hard to get it noticed -- we have the community-nudge feature to somewhat address that.
Looking through Area 51 this morning, I noticed that when there were only enough topics to fill a page (or two) I could reasonably evaluate whether there were topics that I would be interested in participating in. I couldn't force myself to get past page 3 this morning, and honestly I only scanned the topics.
Unlike SO where you only need a few interested and knowledgeable people to provide an answer, and thus a relatively low number of views is acceptable, Area 51 requires a high level of participation on a subject just to progress beyond the discussion phase. I wonder if limiting the number of open proposals available for discussion/commitment at any given time wouldn't actually be better for Area 51. Or, perhaps, change the interface so that the number of proposals shown is limited by default.
The way it is now, there seems to be too much going on in the definition phase. There are over 100 proposals, each proposal has dozens of potential questions that seek to define it. Finding even the one proposal that I would want to participate in amid many proposals that will never make the cut seems like a daunting task.
Here is a possibility. The goal of this is to make it easier to find communities that I'd like to participate in and quickly dispose of communities that don't find support (again, to make it easier to find viable communities that I would participate in).
Have a pre-qualification phase where you get a follow vote and, perhaps, the ability to comment on an "elevator pitch" proposal. This would precede the "definition" -- or more accurately the "elucidation" phase -- where the proposal is fleshed out with on-topic/off-topic questions. The interface for pre-qualified proposals could be much simpler so that more items could fit on the page. Essentially this splits the definition phase in two, with the first part gauging interest and the second, and more time consuming, defining what exactly it is that we'll be committing to in the commit phase.
Have search be the default view rather than browse -- i.e., tell me what you are looking for, I'll see if I have anything that matches what you are interested in. This could (and should) be expanded to first return existing sites, then sites under official consideration, then sites in the pre-qualification phase.
Limit the number of sites in the pre-qualification phase to the number that can fit on a single page. Conduct the pre-qualification phase in rounds (say 6-8 weeks each, jk, maybe 2-4 weeks each). If you don't get some small number of follows during this time you don't make the next round. You get 3 rounds before the proposal is eliminated and you have to get some larger number of follows to proceed to the "elucidation" phase. Close each round to new proposals when the maximum number of proposals for the round is met.