Two contradicting thoughts:
1. There were 6 million +/- Garands made. They aren't rare and restoring one that is as beat up as you say might not do it any damage. Both of my Garands are mix-masters, having been through the arsenal refurbishment at least once. They got new finishes on their stocks but I left the "character" marks in the wood.
2. If this rifle is all original, has a few early features on it like gas trap etc, then refinishing it might harm the value. If the father was a Colonel in the army in Korea he most likely did not carry a Garand but an M1 Carbine. The chance of this being his original Garand is slim, but ...