The Crossfire is something of a brick where drag is concerned. The teardrop shape, with the wider area to the front (cab forward), has long been recognized as the optimal shape to reduce drag, although it generally makes for an ugly car.

I think the Crossfire's shape was more a factor of style and visual impact, with a nod to art deco, and the under side/defusers, as well as the spoiler, were actually designed to make the car driveable once it went from concept to production.

They've done it right, though. The end result, by all accounts, is a reasonable stable car at 150 mph.