Definitely publicising the for sale section here should help drive traffic. Site activity must be a tiny percentage of what it was in the good ol' days. Got any stats on that sort of stuff?
It's interesting looking back at a few old threads and seeing how many people are now banned. A softer touch with the ban stick might help too?
Forums worldwide have fallen victim to facebook, it's just a slicker platform especially for mobiles.
On the topic of banned people, we could probably have an amnesty of sorts but at the same time a lot of people were banned for good reason. Some for personal reasons I'm sure but when in someone's house, live by their rules I say or suffer the consequences. It's amazing how many people see the forum rules as an opportunity to test them, I'm very much of the opinion that if people want to act that way there are plenty of other places for them to do it. I run another facebook group where it's a case of "you're here because we allow it" as opposed to "you're here because we want as many people as possible" and it does very well. 1400 odd members and 1100 active members which is a massive proportion. We actually had 2400 members and the group was shut down but of those 2400 only averaged 800 active monthly and now with just over half the people it actually feels twice as busy.