Regardless of mileage, 2008 is a used car in my eyes. We're 1/2 way into 2009. The 2010s will be out in a few months won't they?
I would want 20% off invoice just based on that.
It can't be a used car if the vehicle is never registered. However, you should take in the consideration of the depreciation, that is why the dealership is offering massive discount to the car.
Also, you can't really use KBB since it is no longer accurate under current condition. The market is very unstable and the dealership will do what ever they can to move the car, without having to shut their doors.