Its not new car buyers that matter - its how long the owners down the line decide to keep it maintained or just sell it for scrap. My car will be 10 years old this year and touch wood its not had any major problems and I want to keep it because its the best car I've ever owned. However if it gets to the point where I'm having to pay megabucks to keep it on the road then I may wave it goodbye despite probably 99% of the vehicle still being perfectly roadworthy.
No idea.
The bloat of car weight seems to be coming to a halt. However they're still getting slightly bigger each time there's a new model version for whetever reason. Used to be that there was a large size difference between european and american cars, now - except for a few massive SUVs and pickups - there's almost no difference.