Adrenaline Vault has an article on the sociological aspects of driving games. It's pretty interesting.
Driving games have always been about the fulfillment of socially sanctioned male fantasies.I would expand that to: games are about the fulfillment of fantasies. Forget "socially sanctioned": transgression is a powerful fantasy, and therefore a major cause of controversy. GTA3 is an obvious example, but think of Tony Hawk: you ride around places you're not supposed to (high schools, airports), break stuff, and freak out the squares. The game I worked on most recently fulfills a common fantasy of taking revenge on an annoying neighbor.
Identify people's dreams, illicit or not, and you can create a compelling interactive experience for them. (It's also a good way of thinking about game development: a dream is a high-level concept that you can use to decide what to do and what not.)
Go to a good news agent and look at the magazines, especially those aimed at hobbyists. Identify the expensive hobbies (preferrably involving a little technology so that there is no fear of PCs or consoles): there's your market. Railroad Tycoon appeals to people who like model railroads, Soldier of Fortune appeals to gun nuts. Perhaps there are some untapped market segments right around the corner.