It is likely that the account may still have a last logged in field filled in. I am sure there will be some caveats and their CS will have to account for them, but I am guessing that most on the forums here whom post have at least logged in recently.
This is a good suggestion, but we would have to manually program a plugin and interface for the forums to do that. It may be a possibility in the future once our programmers have a little more time. Right now all focus is on expansion content or improvements to the game itself. On the topic, we are trying some new tools to hopefully reduce the spam posts.
They have an API plugin for the forums that simplifies the work you are talking about. But yes, it does still require time to get it done. Anyways just throwing it out there in case the spam continues to be a pain.