I think that currently there is very little exposure for new site proposals (considering how much traffic sites like Stack Overflow generate). I'm not sure that a large amount of the user base even knows that there is an Area 51 site (even though the hottest questions sidebar does help users discover some of the lesser-known sites).
I think that something highlighting Area 51 better (such as the trending proposals sidebar) would help a lot more proposals gain the followers and interest they need to succeed. What do people think about that?