Keep any original component that is in good working condition, and replace anything that is not. That has been my rule with the Miyata 1000 I bought 25 years ago. As things have worn out, I have replaced hubs, wheels, the entire drive train, the saddle, the stem, the pedals, and a few other things. But the brakes, derailleurs, seat post, and of course, the frame and fork are all originals.
Interesting, I prefer the 25-year-old cantilever brakes to the modern cantis on another bike I own. The old ones are harder to adjust, but stop more surely. There were some great bikes in the 1980s!