A common tactic for promoting an issue is to create an issue day/week, ect. Such as Veteran's Day or Reading Week ect. Perhaps we could utilise this for creating sites. Site creation should proceed as normal outside of this period
One of the problems with getting a site created on Area 51 is getting attention. When Area 51 first started, lots of people were interested and visited the site. I would image now that not many people visit the site regularly. By the time a site finally is created, many of the users will have lost their interest.
I propose that each year that area51 have a special site creation period of length a few days to a week. This should be promoted via email and by ads on the StackExchange network. By getting everyone to visit the site at the same time, it will be easier to achieve the critical mass necessary for a community to succeed.