Personally I think that vent visors may help FE in general if they round out the curve of the A pillar. If you've got kind of a "sharp" A pillar then finding a vent visor design that smooths the transition from the windshield to the sides of the car may help air "tuck in" better, and not get thrown out to the sides so much, making a wide wake up front.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice