Keyboard Letters Wearing Off?
You may be able to put a couple of coats of mod Podge on the ones that are starting to wear this should stop it from getting any worse. If I were in your situation I would touch them all up with a black paint pen and then put mod Podge over them. Good luck...
Repairing the Finish on a Table?
You can buy paint pens that are the same color as your furniture for touch ups. Most furniture stores have them and I have even seen them for sale at dollar stores. Good Luck.