Rare?
I would say that every painting is technically “rare” since its unique.
As an artist of mediocre talent I get what you're saying, and it's flattering, but by your logic there's nothing special about a 1933 Bugatti, since almost everybody has a car.
Yes every painting is "unique," but post-impressionist masterpieces by highly renowned artists that happen to be for sale are far more "unique" than others.