I feel like this will be true of most expanded social networks, unless the founders value curation and quality over quantity. Some solutions that I can think off may be:

1. Make it invite-only? I don't use CS but I think it had this feature the last time I heard about it. Wonder why it doesn't address the complaints of blank profiles, etc.

2. A group of moderators amongst local users who can verify or address endorse people from their area.

I don't know if either of these will help address some problems which seem to be heavily localised to specific areas though (NYC / San Diego, from what I've read in the post and this thread.)