what would i find them useful for?
as far as i'm concerned, the vast majority of threads aren't worth the time to go searching through the archives to raise from the grave. i occasionally seek things out, but not for the purposes you think of. for example, if there was a flurry of discussion about "wouldn't it be great if moz started releasing non-album singles again" and a few weeks later it is revealed that moz has a brand new song that he is touting as a single and that he supposedly recorded with Alain and the gang, i suddenly become suspicious about the coincidence. it's happened a couple of times before where somebody asks a weird question or poses the thought of "wouldn't it be great if moz appeared on Craig Kilborn's show?" and things happen along those lines a few weeks later.
not that i actually sought out any of that stuff. let's just say that if it was a couple of years ago, i would have bothered searching.
it actually does me a favor if somebody starts a new one because if somebody does resurrect a thread, i have to figure out which post was the last before people started discussing it again. i basically click on the thing that takes me to the newest post and i work my way backwards, but then, it's been so long that i forgot what the thread was about, so i have to start over at the beginning and find out what that person was responding to. then i get annoyed and move on.