In theory you could update the old airframes to pretty much new standard with a big spend on avionics. You can't fix the spar carry through issues though, that's just fatigue cracking based on how much and how many times it flexes a flight. A 5 year old 210 could do low level survey flat out and build up the required stress to see cracking vs a 40 year old similar that has been flown gently in smooth air which shows no evidence. Which is why the ATSB recommendations have merit.
Main thing is though, GA world wide, the smaller operators exist on shoestrings and don't want to pay for anything more than they have to. Cheap old plane does similar job to new expensive plane, whats the incentive to upgrade? And there is also merit to saying they will still crash due to the nature of GA operations, new or old.
In car fleets they are renewed regularly with very low KMs, mainly as there is huge tax advantages that most govs implement to prop up car sales. Maybe this should have been brought into GA many years ago. From memory the major tax benefits that were around for ownership of GA aircraft was removed 20-25 years ago, which was a major reason larger twins dwindled from flying club lineups.