Earlier quoted context omitted.
You may have luxury of feeling that way -- most people do not. The average age of the US auto fleet is significantly older than it once was. 10+ year old cars are like 5-7x more common than they were 10-15 year ago. Hell, I drive a 2003 model year car that isn't going anywhere.
Look if Cuba can drive around on their fleet of ridiculously old cars, then it can be done. It just might not be super easy or labor-cheap. I think what GP is getting at is if you start optimizing first for reuse, there's a lot of cars we wouldn't need to build.
1) Increase in total number of vehicles in use (relatively level 2008-2013, a quick google didn't find newer data)
2) Old vehicles taken off the road being replaced by new ones
The net effect of a particular person buying a slightly used car over a new one is basically nothing. The big picture only changes when people are choosing to keep an old car on the road for longer.