How could it possibly look more aggressive without vents or scoops, in your opinion? I don't see how it could change much at all for the better, really. The ones with vents and scoops are tacky on the 636.
As far as I'm aware of, there are only two cowls. One is made by Kawasaki, and the other is a POS ebay cowl with scoops and vents. Stick with the Kawasaki cowl.