"which becomes uneconomical at least in the resale sense at some point in time, because the repaired car resale value is less than the cost of repair."

I think this is a common misconception about car repair economics. The question is not whether the repair cost is more than the value of the car, the question is whether the repair cost + sale cost is higher than the value of the repaired car. I like keeping cars that I know the history of, even if the car is worth <$2,000 and the repairs >$1000, because it is unlikely that I can get a $3000 car that I have as much confidence in.