Warning: thesis ahead
I like basket-case pins because they're cheap and I don't have to agonize over whether to preserve or restore. I restore, replace, repaint as cost- and time-effectively as I can because I want to experience the machines as they were, and I don't care if they don't look their age. The graphics themselves are the age indicator for me, not yellowed varnish, cracked paint or creaky mechanics.
Sometimes I'll touch things up because it's quicker/easier/cheaper than a full repaint, but what I would prefer is to take it all apart, or strip & make it perfect, i.e. as close to what it was as I can. But touching up well is really hard, and the touchups will likely age differently than the original finishes, making the repair work obvious and unsightly after some time has passed. Know your skill level, etc. but very few can do it right, "right" being in an archival sense. And it takes SO much more time & money.
Here's a case of academic overreach, IMO, on a backglass restoration:
I wonder how much time & money this took?
This is where things will go if we let preservation mania creep too far. Is someone going to bitch that you didn't use a mass spectrometer to analyze the touch-up paint for historic accuracy? It's inevitably going in this direction anyway, as pins become ancient artifacts, mothballed behind museum glass, but I think we should fend off this kind of preciousness as long as we can, and enjoy them.
I feel that at this stage in the history of pins, to preserve or to restore is really a personal preference, and open-minded people would ideally respect this. Players and collectors have different priorities. Some want to maximize collector value and not gameplay, others just want to play the darn thing as it was meant to be played. Resale value and stewardship are not as important. A majority might agree on one approach or another, but it that reason to condemn others?
Another big question is, how much time & money can one invest in a project? Should a beginner only take on a plentiful/undesirable/basket case pin because doing a rare or desirable pin "wrong" might upset others? Or if they can't invest in the "proper" tools & techniques to do it "right"?
As much as I may cringe as a poorly-restored or over-restored pin, I have to remember it's my own personal opinion. People who think there's a truly a right and a wrong way probably don't realize to what extent their thinking is influenced by past and current theory on art & antique preservation. Opinions on this have changed a lot over time, and will continue to change. And then we've got the added twist that pins are machine AND art, so it's more like antique cars, as some have pointed out, with all the categories and sub-categories from that field of collecting.
.....In the 1800s, Viollet-le-Duc, a prolific restorer of French Castles wrote: "To restore a building, is to reinstate it in a condition of completeness that could never have existed at any given time."
I guess that's my approach on pins.
And then in the late 1800s, folks reacted against that approach, called "Scrape":
....."Scrape bred Anti-Scrape, the stance immortalized by John Ruskin and William Morris that forbade all intervention."
And folks thought we should just let it all decay.
And it continued to evolve.
(Quotes from Decay and Restoration in the Arts: https://books.google.com/books?id=4m6NAgAAQBAJ&pg=PA20&lpg=PA20)