There are users and there are collectors. To a collector, a camera might have less value if it does not have the original box and manuals, even if the camera is in pristine condition.
I’m a user. I have a used Olympus Pen FT that has the previous owner’s name and social security number engraved in the top and bottom plates and has a small dent in the top corner. I bought it to use it, and the price was good. After a number of years, the meter began to be erratic (the semi-silvered mirror was loosing its silvering), so I removed the meter and put in a full-silvered mirror (and also removed the self timer, as the lever was snagging on my clothes). For me, it now works better than the original. I still have the parts that I removed, so I could restore it, but I doubt that I ever will.