Get it. This is coming from someone who purchased a prebuilt car already on the lot. Though I am extremely happy with my car, the only thing I would change about the car are the seats, since it did not have the sports package. Frankly, the main difference are the bottom side bolsters and the part the expands forward to support the knees.
Personally, I could care less for anything else the sports package has to offer, which is why I purchased the car the way it was configured, but the seats alone are worth the extra money! I know I will end up buying sports/performance seats as soon as a set comes along.
'08 e90 M3