As far as GM beaters and cars from the mid70s to say 05, there isn't much rebuilding them yet. There are some exceptions, Buick GN( and other platforms), Pontiac Fiero, Jeeps. Also, Nissan had a 240 sedan. The ricers really like them.
I will say my 96 Contour had 214K on it when I sold it. It did not use any oil, even with 8K or more changes. It has 230K when sold next.
Still, the W123 has thick sheet metal. Still, see a bunch of MB W123 around. A lot of Jeep Cherokees (84-01).
I have experiences the to many car to take car of them. The '98 Neon was carted away a few weeks back. Just to many fixes. They might have been easy. I put a bunch of money into it. Body was still good. Trans electrical issue.