It's dead easy. WIS's like old watch to look old on the outside with a perfectly honed mechanism inside it. Keeping your watch looking its age will increase its value.
If you allow Rolex to spruce up the watch, it will come back looking better, most people will think it looks great, but the people who actually buy the thing will consider it defiled and the value goes down.
So that's it in a nutshell, no more to say.
I got a 1655 that looks knackered and had I spruced it up, I would have devalued it. However it bugs me to wear a knackered looking watch.
I suppose the final gambit it that once you have spruced it up, that's it, no going back and that is why I did not spruce it up.