Oldsmobile could be a great brand if it were to be handled intelligently. I'll partially agree with you in that the killing off of well known nameplates may have doomed the brand, but the cars were typically good. The Aurora was a great car for the time. And the Bravada was introduced in 1991 as a Blazer rebadge, so it wasn't really replacing anything. I'd say the Bravada was a great thing for Olds. I think the Alero could have been a good car if it didn't have the electronic issues that it did. It still sold very well. The Cutlass name should have remained, but the 88 and 98 nameplates honestly just sound dated. They give the brand the old Buick stigma of being an old person's last car. And since the Achieva was introduced in 1992, after the Bravada, it really doesn't make sense for you to say that they should have updated it when you say the Bravada was an unknown name. Achieva was even more recent. As for the logo, I can't imagine anyone liked it, but it certainly didn't kill the brand. I'd have refreshed the old logo a bit, but that wouldn't make or break the entire brand.
Pontiac is a soft spot for me. I'm a huge Pontiac enthusiast, and GM's slaughter of the brand still saddens me. Pontiac shouldn't be a racing brand, but you're on the right track. Pontiac was, for many years, GM's entry level performance brand. That means high performance, low MSRP. That doesn't mean that there's no place for things like the G5 or G6, but they need to be done differently. The G5 shouldn't have been such a blatant rebadge of the Cobalt. And it certainly shouldn't have had the Cobalt SS's turbo and supercharged engines, considering the Pontiac brand identity. The G6 was honestly a pretty good car, and the GXP was enough to satisfy the affordable performance criteria.
Saturn really doesn't need to come back. It wasn't an awful brand, but it was just a recent invention of GM to try to compete with imports. The brand started producing cars in the middle of 1990. They just don't have any brand heritage, and the brand identity was cloudy, at best. The only identity I can give them is Chevrolet's old image: the baseline. Saturn needs to be a budget brand, and they need to stick to a very specific range of vehicles. They were too eclectic for what the brand should have been. While the cars they made were of good quality, they didn't make sense. Why did Saturn need the Sky Redline? How did the Vue fit their brand image? Good cars, but illogical.
Hummer needs to stay dead. No discussion. Hummer was a worthless brand.
GMC won't be killed off, as much as I wish they would be. The fact is, they do sell a great many trucks. Their upmarket SUVs remain popular as well. The trucks just leach Chevrolet sales, and prevent GM from claiming to have the best selling truck (which they usually do, when combining GMC and Chevrolet sales). Fun fact: The GMC Terrain was originally a Pontiac, but the car was given to GMC when Pontiac's demise was imminent.
I don't disagree with you on everything. But some of your plans aren't properly motivated. I'm surprised that you don't mention Saab anywhere here. Seeing Saab go was a terrible thing. And if you have Saturn, why not Geo? GM brought Geo out around the same time as they did Saturn. You've got good potential though, because these plans, although not altogether complete or logical, do show a great deal of thought put into them. I remember when I was 16, Pontiac still had a couple of years before they were to be ended, and nobody ever suspected. I had very similar thoughts to yours when I was 18, only then we thought Hummer would be bought by the Chinese, Saturn would be bought by Penske, and we were holding out for some private investor to swoop in and grab the rights to Pontiac. Sadly, none of it happened.