To calibrate the M6's rangefinder removal of the dot is necessitated; I guess they just found it easiest to put a new dot on as opposed to preserving the original Leitz one.
I'm not sure on the value of this slight anachronism, though.
I've never managed to remove a red dot without destroying it.
Don Goldberg did that OK with my early M6, but in answer to the OPer's OP, I don't think I'd worry at all about collector value. Even never-opened-still-sealaed-in-the-box-we-had-to-Xray-the-box-to-prove-there's-a-camera-in-it M6s don't collect that huge a premium.