My notion if you drive an older car with much simpler cheaper mechanicals and manual transmission, then only reason to get rid of it is if the body/frame is getting unsafe from significant rust.
Course I do ALL my own car repair and have time to shop around for best deal on parts. Not opposed to some re-engineering (I weld) if its significantly cheaper or more convenient than original. Hotrodders have done this for generations, just they dont usually make practical daily drivers. But no reason somebody wanting a practical daily driver cant.
Lot modern cars, its the automatic transmission going out that is the death knell. They have become very complex and super expensive to rebuild or replace. Thus my preference for only manual transmission, the more robust and heavy duty, the better. Though they have become rare as hens teeth on anything newer than 20 years old. People that can pay crazy new car prices want all the luxury options. Dealers make more on cars with luxury options so dont stock stripped bare bones models. Thus nobody buys them cause they arent easily available and then since nobody buys them, the manufacturers dont produce them. Vicious downward spiral. No doubt market will correct when we finally end this second gilded age nonsense. Not everybody can be Big Daddy Warbucks, nor can they buy fancy luxury mobiles on credit forever. And those luxury mobiles tend to be very complex and expensive to repair when they get cheap enough for joe sixpack to buy. Govt wont let you simplify them to make them cheap to repair, want everything strictly factory issue.