And it doesn't necessarily have to be either of those choices. "Pretty and perfect" is the preference of railfans, whose primary interest is having the equipment available to be photographed, and many of whom are notorious as a group for not contributing effort or monetary support to museums. Things that are under restoration or even in parts are far more interesting to the general public, who come to the railroad museum for a look at things they cannot see so close-up in their normal access to railroads. And the general public includes entire families, and they spend a lot more money at the museum than most of the railfans ever will, and won't be nearly as fussy about all the small details of the exhibits.
"We Repair No Locomotive Before Its Time"