I doubt the submerged NACA thing is really it... But on the subject of s. NACA's - if they're shedding, they're improperly used/designed... The flow exiting the duct should be sufficient enough to prevent that from happening.... At least, that's what the research we've been doing has said... That, plus shedding makes noise :/
As for the roof line ridges.... One really can't ignore the structural advantages.... The geometry is stronger - so a thinner/lighter material can be used... That on top of aero benefits. Furthermore, flow over the center will be faster than flow over the sides due to interference/spillage over the side of the car.
As for the vette.... I'm sure this isn't hurting
