A while ago a business manager I work with purchased 30 exact match domains, willing to use them for "SEO purposes". I actually poked around for ideas here too. At the end I decided I can't use them at all and got them redirected. The advice I got here was to focus my effort on the main site. What I plan to use them for at this point is AdWords. I will try to boost the CTR. If that does nto work, I'm 301 tem to the main site again.
My plan is to grab the domains, put a canonical link element on the whole domain, since it will duplicate the main site. Since AdWords URLs tend to get pasted into forum threads, blog post and social networks, I'm kind of hoping for a collateral effect in terms of backlinks.
Even if you have your sites reincluded, there is no guarantee that they won't go down again pretty soon. This seems a short term strategy anyway. Get the good URLs redirected to you main site and focus your effort there.