It's probably been suggested before, but here it is anyway for the suggestion box:
I think 'similar threads' are causing people to revive old threads as it's easy not to notice date of last op update, or first op even.
Maybe if a heads up message at top of op like the one we get saying MN has commented that it's a 1 month or 3+ months old thread. Maybe have a different colour for old ops than green. I know post colours can be edited but those who know how to change the settings probably less likely to click on similar threads and not check the date...