You might want to put in one of your URLs here http://spyonweb.com/ and see just how easy it is for anyone to spot the servers that are on the same IP or that use the same Google Analytics or Google Adsense code. If we can do it that easily, so can Google.
What is your content like on these? Do you have enough content to make each site unique and standalone? Or is it worth the thought of combining some of them like others have mentioned?