I'd like to point out that I have purchased NIB vintage blacks, and I find them to be much scratchier than used vintage blacks. I guess how hard they are used really has a large effect since I have some mx blacks from a 2004 cop keyboard. They are smoother than my NIB vintage blacks, however, used vintage blacks are the smoothest. I can't comment on the new mx blacks since I don't have any yet, but I can compare them if I ever purchase them.
On another note, does anyone know if all mx nature white switches are new stem? I think Zeal commented that they were, however, I got a user to open one up and the stem was not angled like the new stems.