There's "fixable in theory" and "fixable in practice". As a former gearhead, I'd argue that cars from the late 70s/early 80s are effectively unfixable - it was the era when emissions standards were ratcheting up, but controls were still mostly analog. Engine bays were a giant morass of rubber vacuum hoses that nobody sane wants to deal with anymore.

Mid-70s and earlier cars tend to be simpler, but they would never pass modern emissions tests. We picked clean air and fuel efficiency over simplicity. I don't think this was wrong.

It's really hard to know what to think about the direction cars are heading. Yeah, there's a lot of closed software and electronics. On the other hand, I have at least one friend with a hacked Tesla. And the huge emissions regulatory and inspection regime that prevents you from making changes to engines doesn't apply to electric cars. So it's a mixed bag.