Devil's Advocate
From a seller's perspective, you lose exposure and focus by using a generic thread that will be mucked up with all kinds of ads interspersed with questions and comments on any one of a numbers of items such that you literally "lose the thread". As a seller, I want to put my offering out there and be able to watch a thread for questions that pertain to my offering, get it sold and then watch the thread drift into obscurity.
From a buyer's perspective, you're left to sift through a whole bunch of stuff that has no interest unless you're just window shopping and looking for targets of opportunity. Again, as a buyer who's looking for a used Santana, I'd appreciate having the chance to 'see' that Santana F/S message topic pop up as a new subject instead of having to sift through some mega thread in the hopes that the latest post was something of interest.
My recommendation, if it ain't broke don't fix it. I think the mods have embraced the fact this fairly low-volume, niche forum of ours doesn't see any classified ad abuse and, that being the case, lets the infrequent private seller ads run their course without moving them to the larger classified ads forum. That's a good thing in my mind.