If you had a strong air blower in front of the car, would that improve aerodynamics? And if so, would the energy spent in blowing the air be less than the energy lost due air friction when the car didn't had the air blower?

I've also considered some retractable plastic covers, that would stay inside the car when it is parked, but would unfold when the car was in motion. These covers would produce highly aerodinamic profiles; this for cars that are not very good in this, where designers chose aesthetics over aerodynamics. But this variant is a bit messy. 

The apex of this idea would be to use a Star-Trek like shield. It is a shame we don't have that and it just seems out of our reach. I tried to come up with a way to make them real in a number of occasions. Confining gases or any other ordinary matter with energy would really come in handy.