IIRC, Saturn was supposed to be a distinctly different brand intended to go head to head with the Japanese imports, such as the Civic/Corolla/Sentra on their ground in the US market by copying their ideas & business strategy, but that & the cars weren't quite up to the task, and the last few years, say about '02 onwards, the Saturns lost most of their distinctiveness, succumbing to the homogenizing effects of becoming yet another take on GM badge-engineering. As a result, they became superfluous, and thus disposable when it came time to downsize the company in bankruptcy.
The issue, from what I've heard, is that GM wanted to push Saturn upmarket with new products from Opel, but the issue was that they were more expensive, and so lost Saturn's original customer base, without really being able to replace it due to traditional GM failure of advertising. (Pushing Saturn upmarket also meant that it stepped on the toes of Olds, hastening its demise, I think, as Saturn was at one point favored at GM)
I think Saturn was a mistake- huge amounts of money were expended on a new brand that only served to compete with Chevrolet, while the money that could have been spent on the existing brands for product was also sent away. In the end it never made GM a cent, either, even if it did attract some import buyers.
With Oldsmobile, I haven't really seen any vintage advertising, so I'm not sure what their traditional identity and niche outside of the old GM strategy of having an increasingly prestigous selection of brands one would progress through as one became more finanicially succesful. I think they were aimed at younger professionals and middle to upper-middle class people who wanted a near-luxury car, more prestigious than a Pontiac, but with a bit of sportiness and without the stodginess of a Buick, which has a reputation as a car for old folks and successful but boring people like accountants, yet weren't quite ready or interested in a Cadillac.
That's what I have found as well- more performance and technology than a Buick, more luxury than Pontiac. But this is a very squishy section of the market to be in... especially when the imports started their own luxury brands that grabbed a lot of the market, which I think destroyed a lot of the "above entry-level" market that GM's non-Chevy brands had played in.
When that strategy collapsed, Oldsmobile was kind of lost in the middle, and although GM did try repositioning the brand as a luxury/performance brand, the effort failed because the cars weren't up to par in either department- styling, interior, and driving dynamics were still corporate meh, not to mention the epic fail of what's supposedly a sporty car only being available with a slushbox, especially if it's already hampered by being saddled with a FWD platform. Furthermore, that half-assed effort failed to provide sufficinent distinction from Pontiac or Buick as they didn't have sufficient in mixing performance and comfort to entice the performance people from a Pontiac, nor anything to keep the more luxury-minded older people from going to a Buick as they traditionally had.
Well, I don't think inter-GM competition was necessarily the only problem- the introduction of the Japanese luxury imports- Acura, Infiniti, Lexus I think were just as big of a hit to the brand.
Another issue, I think, is that they found the "Oldsmobile" brand an embarrassment and didn't even put it on the cars- I remember several times seeing cars labeled only "Aurora", and for awhile I thought there was in fact an "Aurora" marque- it was not until much later that I realized it was an Oldsmobile. Now, I was pretty young at this point (definitely not in the market for a new car, haha), but I think it still says something...
