The air diffusers are called vortex generators and they add energy to the airstream. Some aircraft use them on the leading edges to make the air "stick" to the wing at high angles of attack to delay the onset of a wing stall. The pics in motor trend show a smoke trail test with and w.o the generators and they actually work...The z already has an aerodynamic shape, so I doubt it would do anything that the existing spoiler doesn't.