Splash cork bar-tape should take about half the value off any vintage lightweight.

Seriously anything you change that cannot be changed back with a wrench, screwdriver, or black tape will hurt the value of a collectable bike. But taking off original tires, wheels, brake pads, brake hoods, freewheels, etc. so you do not burn them up by riding the bike is actually a good idea. As long as the original parts are stored correctly and re-installed when you go to sell the bike.

And, hi-end 70's and early 80's Treks are bringing real money now. Whoever sez no is not paying attention.