If a thread is inactive, and has been inactive for a month, then that'll be because people lost interest and just let it die. There's a reason for it being inactive and expired.

If they're a clever member, then they'll ask why they couldn't reply to the thread, and a staff member will probably bump it for them. If they're not, and just leave because of it, then there's a good chance that they're the type of person that posts a few times, and scarpers.

Also, do we really want things that were topical six months, a year, two years, four years ago being brought up again, when people will probably not care about them?

I've personally never seen the need to post in an expired thread. If it's on the same subject that I might have posted a new thread about, then I'd read through, see if it answers my question, and if not, post the new thread. If it does, then no new thread.