I have replaced almost ALL flipper assemblies on ALL games, and when I do, it makes me *very* happy. I have skipped a few flippers that have short range shots (shots that don't require a ton of power), but I do have the assemblies ready for them, when I have the time to replace them.
I would say out of the 32+ assemblies I have replaced lock stock and barrel, roughly 3-4 seemed to be in good condition when I did the replacement. The other 90% of them were plenty worn. Bear in mind my pins are 25-35 years old.
It's like getting new shocks or new tires for your car -- your ride is much better. Sure you "could" wear out the old stuff and save a few pennies.
But did you get in the hobby to "postpone maximum joy" ???
-mof