This is quoted from the VAC FAQ section:
Q: Will newer vintage Airstream skins polish as well as old skins?
A: Yes. The pure aluminum alclading that allows the skin to take a high polish was used up until the middle of the 1982 production run, when the finish was changed to a satin finish.
So it's only '82 & newer that don't polish as well...I believe they started using the satin finish because it didn't show production scratches as easily.
The concern with polishing alclad skins is in not over-polishing through the alclad layer. The composition of the aluminum underneath would have a slightly different color and oxidize differently than the remaining alclad portions.