If the hood spacers actually "suck air" then they should function on the same principles as a Cowl Induction hood of muscle car fame. It creates a pressure difference at the base of the windshield which allows the air to be sucked in more quickly than the standard flow path. I'm sure someone can find the actual principle and such. I'm just spewing info I recieved as a kid, looking at a Camaro SS, and saying, "Dad, why is the hood higher in the middle like that?"
edit: Hahahaha, what he said! ^