Agreed with the above, I'd say its cheap, almost too cheap that people may think you are looking for a quick sale before it goes bang. (Which I assume you are not?),
I would also say AutoTrader is not the best audience these days. eBay is very good, but you do have to wade through the odd scammer and stupid offer. My last 2-3 cars have sold through Pistonheads - I would give them a try and you can also write a decent advert and not just the few paragraphs AT allow you.
GLTWS