I believe it is still in the rules to be
thoughtful of others. Reviving old threads with nothing new to say or misleading other members would go against that so it's kind of covered. I think the issue really is one of enforcement since such things are usually done by the same offenders. Don't be afraid to report posts, but the moderators do work hard so also be mindful of them.
The funny thing is, it IS an unwritten rule of forum conduct. Some just refuse to follow it, so it isn't so much of an implementable act, but rather something that is to be gently discouraged. If you can gently pull someone aside in a conversation and say, "can you please be careful of that next time" and said member agrees to those conditions, there's nothing to deal with. Like you said, it is the actions of those who continuously do that that that is the real problem.
It is first and foremost an issue of politeness and thoughtfulness, especially if it's about a long abandoned project. Especially if we're particularly cheesed off the project didn't happen.
Let's say a noob posts something about the Muppet Reality Show pitch from a few years back. We'd immediately assume... NEW POST?!?! Gasp! That can only mean that A) something's come out of it, B) someone has details or even better C) someone has footage that was leaked... only to click on the link to see an entire quoted text for a whole screen, and a typo filled "i lieks da ice creems" message.
Wouldn't you feel the need to throw the keyboard at the computer screen?
However, I've come to a realization... maybe it's other message boards to blame. Some have a VERY strict policy about multiple threads, causing new threads on the same topic deleted or blockedby moderators, sometimes who link them to other threads. I've been on one forum that did that, and it's apparently a huge pain for their mods... so in a way, maybe these guys are conditioned to actually do something like that with old topics. So maybe it isn't quite their fault after all.
Again, we come to the question of which is more acceptable... bring back an old thread or creating multiple ones? Now, I think if there's anything older than a couple years, that means the conversation has long since ended, and no one has added anything to say. In that case, there's nothing wrong with starting a new topic. We've probably forgot we even had that thread in the first place.