Just a thought about a logical flaw. Since the car moves and turns, the light reflections change: so, whatever light source is considered when pixelling the car, it is bound to be not correct most of the time. Of course fixing this problem is possible only using real-time rendering, which is obviously not what I'm suggesting here. What I'd suggest is that you use a more "neutral" position for the light source than the current one (top-left) - f.ex., given the perfect top view visual, I'd go for a perfectly centered position. The downside could be that the car would look less interesting, but maybe some good pixelling can take care of this aspect as well
saimo