Anyone saying that Web 2.0s, new and expired ones, are not working (including tumblr) is either not doing it right, or need more link power. Don't expect miracles, but they can certainly help. Expired ones kick in faster, but if you do new properties the right way and are willing to wait a bit, then they are quite useful.
That being said, I wouldn't fully automate search and registering. I would like to check number of links, type of links, ref. domains, etc before registering. Of course, you could also register them all and later choose which to use. If automating this, then some filters would be useful, like MOZ or Majestic or Ahrefs data. I populate them manually always.
For now, one can always find expired tumblrs or other web2.0s, filter them based on preferred criteria, trim them to username, and then use those to register them with a tool of your choice. In rankerx you can put usernames in spintax format and then try to bulk register them.
