A lot of my engines date back to the 70's and 80's also. I got my first prop balancer in the mid 90's and I think I've balanced maybe 3 or 4 props so far, mostly out of boredom, but there was at least once when I cut 1/4" off of each blade to shorten a prop at the field with a razor saw. I balanced the prop that evening after a days flying, and the next time I used it, you really couldn't tell a difference.

If you really want to keep your engines in good shape, avoid using them for landing gear.

*Amusing side note: At one point last Winter I had nothing to build and my shop is the only place in the house where I can smoke (wife's rules). So every time I would go for a smoke, I had this prop that I was balancing. I used to have to balance high-speed grinding wheels, so I am familiar with the Dynamic balancing technique. So just to pass the time, I balanced this prop until it was PERFECT (or at least a perfect as humanly possible) First flight last Spring, you guessed it, Hit a pothole and broke the prop on takeoff!