Well of course, I was just making a generalization. In reality, any aero piece that is added for on track performance will need to be wind tunnel tested to be finely tuned for maximum performance. Not many people can afford that though.

Personally, I think that street cars dont need wings and splitters to be good track cars unless you are pushing GOBS of horsepower and pushing past the limits of your suspension/tires where you would need aero grip to help you corner at higher speeds, but smoothing the air flow under the car will always help reduce your drag coefficient.