Don't forget that Google has neutered the PR for a lot of inner pages in sites, especially if they are directories or duplicate content pages. They may have nullified some of the the links pointed to your sites, which would reduce the net effect of your link building efforts.
Will, how can you possibly keep up with 1,713 domains?!!! It looks like your stable of sites has doubled over the past two years.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin