I've seen a 45K miles 05S car being advertised for sale by the original owner for $55K over a year ago. It still had warranty and basically no dealer visits other than maintenance.

I'd suggest you wait a few month. The 09 cars will be here shortly with even the base cars rated at 345 bhp. That is bound to devalue the used S-car market. When a brand new base car with 345 hp is selling for just over $70K, it would be hard to get more than 50K on a 3 y/o model.