The main problem is following: you replace 20 years old capacitors that can work 20 years more to new ones that can work just for 3 years. Sometimes old parts had much better quality than same new parts.
Preventive maintenance or wait till it breaks?
This is more focused on older gear- do you run gear until it's showing obvious signs of problems or do you do preventive maintenance before problems appear? I fall into the preventive maintenance side as I replace capacitors that are 20 or more years old.