GM is gonna need a whole lot more than some billboards to even get me on to a dealer's lot, much less sell me a car/truck. I have owned all gm except one car('89 Mustang 5.0) and one truck('92 F150 and their dealer made me trade that in on a '94 Chevy pickup).
A decent Rear drive, sporty car with a trunk would be a start for me. (Two door G8 anyone?)