While drive by posting from people who don't know what the game is can be frustrating, I don't get the angst for car modifications. Sure adding a spoiler 20" wheels and a anime livery to a civic is what some people get off on, but intelligently modifying a street car to gain performance on the track is fun and rewarding.
Its not angst, its just not the point. These cars are based on real world counterparts and modifying them, beyond what you can do in the pit, means fudging the numbers.
Its like adding different engines to an A-10 in DCS. The point is to fly a simulated version of the actual A-10, not an A-10 that doesn't exist.
Along with not being the point, you also have to consider that by detailing a specific car's attributes and characteristics means that changing a spoiler would effect many more variables and probably not have the desired effect.