I am not sure which type of spoiler you are speaking of, but i am referring to the type which reduces the aerodynamic drag on an automobile. A true spoiler is intended solely to improve fuel economy as it reduces the negative pressure behind the vehicle (similarly to a vortex generator. Downforce is generated by a wing (in the opposite direction as on an airplane).
Note that on the FC, the Aero package reduced drag (CD from 0.31 to 0.29) and included a spoiler.
Maybe they do something different on an airplane.
You don't have to take my word for it, please do some research:
This will get you started:
Spoiler (Automotive)