Spoiler is needed for aero purposes from what I have read. Front end lift was a major problem in testing.
From interview with Jeff Gale at
http://www.nytimes.com/2008/06/15/au...=y&oref=slogin
“We wanted to keep the recessed grille,” he explained. “But when we did the first 3/8-scale model and put it in the wind tunnel, so much air was pushing through the nose the hood blew off. Bits of Styrofoam and clay were everywhere. We knew then we had a big challenge.”
To balance the airflow, Mr. Gale put a small spoiler on the trunk lid and an air dam below the car’s nose.