There is NO reason for a spoiler on any non-race car, IMO. ALl the asian kids have them on their little hondas. They are about 100 mph short of needing one. But boy, those fancy mufflers sure sound fast!
My new mustang has a spoiler. It's called my wife.
You live in the San Joaquin Valley too?
all the asian kids?
hell try any teen that has any type of Hyundai, Toyota, Honda or Acura....
Disclaimer - most of the spoilers and wings out there are set at either zero angle of incidence or a slight negative value and have no value whatsoever. And, most of the aftermarket ones are hideously ugly anyway.
That said, a spoiler comes into play at about 50mph. It can either be used to plant the rear end of the car, clean up the rear aerodynamics, or both. As an example, TWR put a small spoiler on the back of a Jag sedan in the 80's and cut drag by 18% while increasing downforce. Try driving a spoilerless 84-89 300ZX on the freeway sometime, then drive the spoiler-equipped version. It does make a difference.
Here's the mathematical explanation for you:
There is an inverse relationship between the size of the muffler on a Honda & the size of the johnson on the driver.