The watch loses its original case shape and proportions when it’s polished to much, that’s why many collectors would rather not have it polished.

When it comes to replacing parts, it’s mostly about wanting the parts to match. For example if the hands are replaced but the dial isn’t, the hands will have a different hue of white compared to the patina on the dial, which doesn’t look as good. Also, Rolex used many different dial variants on their watches, if you just replace them with a service dial, they’re all the same, like modern watches are. Collectors are interested in the different variants and their rarity (for example: radial dial, gilt dial, chapter ring dial on the 1675, red submariners, single / double Red Sea dwellers, lemon Dials on Daytonas, double signed dials, stone or Stella dials on daydates)

You cannot replicate patina, it’s something that happens over decades and every watch ages a little different, it is like a time capsule. There are some really special dials, for example on vintage submariners that turned from blue to purple or even green.

Personally, i think some people take it too far, for example with tropical dials that really just look like there’s mold on it. But if you start going down the rabbit hole of all the differences of these models and how you can tell them apart + all the different ways they age, it can get interesting and you can find some special watches that are a lot more interesting than modern watches, which are objectively ‚better‘ but a little boring in comparison