Not having seen the wind tunnel testing myself, I'm dubious of any claims that the shutters are not functional in aero. Isolating the discussion to and focusing on the us of the shutters (which I know the engineers surely didn't do), it's difficult to necessarily know how they effect aero. The assertion that they actually cause worse aero by forcing air under the car sounds very dubious to me as they've got a "skid plate" type deal between the front of the bumper and the radiator core support, and then there is a deep airdam at the face of the radiator core support to force air around to the sides (assuming path of least resistance), not so much under. Typical wisdom for this is that using a deep airdam before the engine compartment creates a low pressure zone below the engine compartment, thus allowing hot engine air and excess underhood air pressureto be evacuated very efficiently. Given that the ST is intended as a performance vehicle and rated to a computer regulated 155mph, I think they'd take significant steps to avoid front end lift at speed. I intend to actually see how this works out in real life by doing a standing mile event or similar, like maybe the long straight at Sebring, and we'll see.
One last thing, speaking of blocking air... at every top speed event I know of, it is common practice to tape up and block as much airflow across the front of the car, especially on the blockiest of front ends, to the point of often causing engine overheating. The result is usually at least a few more mph on the top end. I believe that has more to do with the aero benefits of blocking all that air than with any contributions to engine heat control, and that's what I've been told by the racers that do it.
Just my .02.