I have seen some aliminium discs on some older bikes that I actually wouldn't have taken off because they really did seem to suit the look of the bike. They served no practical purpose as the limiters were properly set but they did sort of look good.
I've never seen plaggy ones that look good and imo should be taken off and flung into the recycling bag.
I think the really important thing about the plastic ones is not so much who takes them off, just as long as they are taken off.