When we traded our Hyundai in on a new '10 Nissan, the dealer told us that two tires needed replacing on the Hyundai. Yeah, whatever. I thought to myself " it also has 190K miles ". They are going to give you as little as possible on your trade and I would venture to say that you wouldn't get your $400 investment back from them. Either trade it now as-is or get some used tires on it to ride for a few months. Dont ride with the bald tires. If they are bad enough that it is concerning you with the trade then they are bad enough to be replaced.