I know this isn't the first time this is been brought up, but is there a reason that threads which have had no activity on them in an amount of time (six months/ a year) can't be locked for new activity? The threads would still be available to search and view if people want to look at them. This is standard on many other forums.
In the Baby Names section, not infrequently very old threads (one from eight years ago has just been revived) are brought back, I can only imagine from search engine results and the poster not looking at the date and replying anyway. The answer often given is that there is a message warning posters that the thread is old, but clearly this doesn't put people off adding their message anyway?