The rule of thumb I like to use is: If I can find a relevant thread, I post in that thread. If the old threads just does not fit, then I post a new thread.
At one time Work in Progress (WiP) threads did not have a timer on them, so new community members would find demos they liked from five plus years back and comment on them. Chances were that these older WiP that have had no recent activity on them were either on hiatus or abandoned for the time being.
Now that these threads have timers attached, the issue is not as bad as it once was.
Over the past year or so, Gower has been merging general threads with the same topics and that trend is a point of emphasis for the moderators still.
The exception here would be if the old thread was so old and out of date with its information that it would create more confusion than anything by reviving.