I can think of several threads that were revived after being dormant for more than a month, to good effect. One example is "The most embarrassing thing I've ever done to earn miles" (http://www.flyertalk.com/forum/Forum1/HTML/001367.html). It started with a lot of activity in June 1999, went dormant, had a lot more activity in October 1999, dormant again, and then (after a post to bring it forward) a lot more last month.

There are other cases where someone posts an update to a situation more than a month after the most recent discussion, and the update generates more discussion. Putting the update in a separate thread would lose the background info so it would require either a cross-reference or a summary.

So, I vote for keeping this as it is. Unused threads drop off the most-recent list anyhow, so they don't get in the way.