...we have polished our '64!
The Alclad layer of purer aluminum on an Airstream is very thin. I would be concerned with going through the Alclad and exposing the stronger, less pure aluminum underneath using polishing compounds and pads that are too coarse. The result is that the underlayer of aluminum is a 'greyer' color than the Alclad which is very 'white'. The two materials will oxidze at different rates leaving a splotchy finish that unless you are prepared to remove the Alclad everywhere, it will be noticeable.
We have a 2"x2" area on one small door panel that we actually went through the Alclad trying to get out a deep scratch...it doesn't photo well, but you can see it in person. It looks like it's still oxidized or dirty looking, which is how it's so easy to think you need to polish it more which actually makes it worse. We plan on replacing that door someday...