I think the problem with splitting the WTB and the WTS is that someone who goes to the current classifieds to post an item for sale would hopefully see a WTB and respond. If you move the WTB into its own category, a seller has to explicitly go there to check.
Then again, if your WTB is buried under two pages, the seller probably doesn't see it anyway.
I think you're right, I don't think a WTB section would be visited too often. There is a firearms forum that check and because of the chance of interstate sales you have to select which state its for. Maybe there is an option for a WTB vs WTS like this.
It might be nice to have a bump rule or suggested bump wait(just to keep messages to the mods down about guy xyz is bumping too much).