I would say the majority of collectors, want them original. They are only like that once as you say. I keep all the nice originals in my collection. The restored motors I sell. I could always restore another, but never find a beauty original again.
I went to an auction where the dirty, gritty originals were going for much more than the fully restored motors. No one wanted them.
Just my 2 cents.
Im not against restoring motors, I do it all the time. But I paint the ones that really need it. I keep the choice originals, choice.