There are a lot and some weak brands, but I think each could be kept and focused (both product and market positioning) much better for success locally and globally.
I'm not really a Chevy fan. I would pick the Pontiac almost every time (Malibu is nice, but that's about it). Chevy is so friggin' bland and common, but it sells. Once Chevy's product is more relevant to me, perhaps I'll feel different about the need for other brands but for now the Bow-Tie is borrr-riiiing.
Pontiac needs to be more authentically sporty and stand-out from the rest of the GM models. It should be performance, aggressive styling, and handling - not just talking about it.
GMC is redundant, but again I nearly always prefer the GMC over the Chevy Truck (exception being the current Tahoe/Suburban). Truck buyers are loyal enough, and really, the product is not that much different that it costs much on the engineering side to continue. Would likely cost much more money to buy the dealers out. With the US following Canada's franchising of Pontiac-Buick-GMC dealers I would hope GMC's position in the US will strengthen more towards what it is in Canada, tho unlikely to get anywhere near the same level there.
Cadillac is becoming quite edgy and progressive, which it needs to be, but perhaps too much so for 'traditional' buyers who don't want the firm suspension and tighter dimensions. Buick should remain affordable cushy luxury (Camry/ES-like), but done better than in the past. 3 models done right is fine with me for now.
It's a shame Saturn is underperforming, but it's probably the brand I'm most positive on, and the one with the highest CSI. That said, seems every time they come out with Saturn the duplicate of it winds up being better - the case with the AURA/Malibu, and I feel the Outlook isn't as attractive as any of the other Lambdas. I hope GM continues with it, and imports/builds in NAmerica true Opel models. Even if not the breadwinner could be a source of passionate faithful followers - more Volkswagenesque but a company that actually provides product we want at the time we want it unlike VW. With Ford set to impress in the next 2 years I think they ought to get their act together and use Saturn to their advantage far more than they have been.
Saab is down and out, but that's largely to do with aging stale product along with problems of dealer network and awareness/consideration. If Volvo's acceptable, no reason Saab can't be and with fresh product it'd probably sell well enough in Europe versus starting from scratch with Cadillac... but Cadillac should definitely be global, and share some with Saab IMO.
Hummer is the question mark. As a niche vehicle, it's fine. Jeep and Hummer have a place, albeit small. But Hummer would need more affordable models to make a true go of it as a franchise, or profitability and not volume would have to be the priority.
Regardless of the outcome, GM does a poor job of platform sharing/cloning. Sharing components and drivetrains is fine, but many vehicles are darn near copies of each other or poorly reflective of the brand's aspirations which just undermines all parties.
