Among the reasons for discouraging bringing up old threads, first is that the people who posted to them are often no longer around, so it’s a one-sided debate. And second, most members dislike having to read through an old (long) thread to get to the latest comment.
So, yes, they just sit there, alone and mostly friendless, although new members do find them and read them from time to time. They are not deleted unless an infraction of the rules is involved.
We have discussed from time to time whether to archive them, and I don’t recollect the decision or the reasons for it. I think the feeling was that they didn’t slow the boards down, so why bother archiving. However, perhaps some moderator with better memory will comment.
I think if something relevant happens, it would be okay to bump. But it would be situational. Like we bump old Enterprise threads on reruns, but don’t bump random threads about puppies from 2001 when we find a puppy (unless it happens to be the same puppy from that thread, then you have to wonder why it is still a puppy after three years).
There’s a guideline in the stickies here that anything older than around three months since last post should just be linked to if there’s a need for comment. If we start sorting out which thread is “relevant” and which is not, making exceptions for one kind of thread, and not another, we could end up with confusion. The guideline sounds good – why not stick to it?