I keep some 5V PS/2 boards to fix my stuff when they go, and when I run out of those, I'll be putting in the PS32 replacements. I also replace any suspect capacitors that I can reach on the 5V boards as one in particular seems to be prone to failing.
I'm in the "run it until it drops" camp, however I do agree that regular maintenance and battery replacements are a good idea. I write the date on the battery when I put it in a 5V locomotive so I have an idea how old they are.