Bingo.
The billions of dollars they are currently spending on incentives and advertising for Hummer, Pontiac, Saab and Saturn can be funneled right into product development and advertising for Cadillac, Buick and Chevrolet. The STS and XLR never took off partly because they only advertised them for a month or two, then left them to the fate of public opinion as espoused by Motor Trend and Internet chat rooms. The average person doesn't know that an XLR-V will outrun an SL550 for less money, partly due to GM wasting money begging people to buy Saturns that they could have used to promote the car.
The Cadillac/Chevy/Buick split into a new company will be the best thing that ever happened to those three brands.