Sounds like you want the sunroof, and that's the important thing. How long will you hang on to the car? the resale value impact will obviously be lessened ae car gets older. One other thing to consider is if the people that like the sunroof are actually likely to be the buyer of your car come resale time. one thing to note, a carbon roof might actually be something an M car buyer is looking for that someone not in the market for an ///M car, however if the person was looking at non-M then they would possibly chase a car with a sunroof.