1. What if the reaction of NPCs to your car and its modifications helped dictate whether they wanted to race you?
2. What kind of NPC "personalities" should we have? Example: NPC A prefers to race when he thinks he can win; he will go up against the most seemingly-stock cars he can see, but he won't check under the hood. NPC B prefers to race against cars with smaller engines, without considering the size or weight of the car.
3. We will inevitably have a "The King" NPC; what should he look for? High-performance parts instead of cheesy stickers? Sporty cars? Cars with chopped tops and shaved-off bumpers?