I had a leased 2004 grand am. My impressions of it were:
-Very nice engine (2.2 ecotech), it had plenty of power, good fuel economy, didn't rattle, and ran just as good in the cold as in the heat. I could see that engine still going 15 years from now.
-Bumpers were pitiful. Someone hit my front in a parking lot, it didn't dimple, it stretched, so it was ugly but no repair was needed. The back bumper was very loose! I think it would have fallen off within 50,000 miles. Seriously, it had a few inches freeplay, I didnt know bumpers had freeplay!
-Body (except for bumpers) was very nice. Strong metal, good looking clearcoat, and the doors were very solid and sealed decently well.
-Transmission felt the same after 3 years/20k hard miles as it did new. 4 spd auto. Easily could have lasted the life of the engine.
-Interior was very cheap, seats were stiff, buttons and knobs kept breaking, and I don't think it would have held up well after 5 years.
So I think that car will still be around in the 20's, but the interior will be shot and various electronics wont work. Only warranty repairs we had done were the security thing, not a system, but it locked the car if someone were trying to start it with a screwdriver or something. Left me stranded 2 times, they replaced 3 times. Also the knob for the heat controls broke, very inconveniently when I needed the defroster, had to stick my head out the window to see my way home.
This was an older model, but I think the same can be said about any GM car. Friend has a lexus, 1993 , everything still works and the car runs like a top, only thing worn out are the leather seats. He also has a 97 saturn, tranny and engine are fine (little rough tho) but the interior looks like it's been through #@$%!(way everything is falling apart), moonroof, defroster, and various other things don't work, not the fuses either.