I know there have been one or two instances where it's been beneficial to let potential buyers know of something that's not included in the OP, but realistically the majority of the bumps on these threads are nothing that can't be done via PM.
ZeroIn disables posting by anyone other than the author and I think it'd be a good idea for that to happen here as well, because I'm seeing a lot of really old thread being necro-posted or just excessively posted on by people who either don't know about or can't be bothered to use the PMing system. Seems to have got a lot worse in recent years where a lot of people are used to Facebook for their buying/selling (and where PMing generally isn't done all that much for initial negotiations). Certainly a little while ago we were getting a lot of "PM'd you" posts - the reason for which I'm not sure as receiving a PM not only gives you a big red '1' (on the desktop site) but also emails you.
It's really cluttering up the 'view new content' and I don't think we'd lose any functionality from doing this.
Also I know the chances of Devastator actually reading this are slim to none, but hey I thought it worth posting here officially because I'm pretty sure I'm not alone in seeing 1/4 of thread bumps coming from the classifieds when they aren't needed.