Blocking would be bad, because there are on occasion good reasons to resurrect a thread.
The biggest annoyance for me is not even the thread-resurrection itself (even if a lot of them are pointless), it's that after that has happened a lot of people will start replying to older posts in the thread as if they're still currently relevant. That happens because the thread appears new (it's on the first page) and not everybody spends time reading the post date of individual posts.
With the current system of replying to a specific post, I think it would be feasible to put up a warning if the actual post you are replying to (regardless of the date on the last post of the thread, which may be current) is over a couple of months old. You might also consider putting up a (smaller, less intrusive) warning if the root post of the thread is old, regardless of the post you are replying to (because you might be replying to a new post that needlessly dragged up an old topic).
But don't block it entirely.