spoiler/air deflector

[socko]

I'm in a rural area . . . lots of dust. My liftback sucks up a lot of dust on the hatch rear window. I understand that this happens because the air flow over the roof creates a vacuum at the back. Air deflectors made for SUV's or what used to be called "station wagons" deflect some of this air downward to counter the vacuum effect. But does a spoiler help with this problem? Seems to me that its purpose is to cause some resistance to air flow thus more pressure to keep rear wheels in contact with road surface for better traction at high sppeds. In normal driving spoilers seem to be purely cosmetic. Would appreciate some advice.