If you plan on using your Airstream to camp in then you will want to "Get rid of the Old and bring in the New" so to speak. The only question here is how original do you want to keep it? In doing this I would replace old mattresses, maybe the curtains, and the flooring if it needs it. I would replace the light fixtures with new ones that are of the same era so as not to mismatch the year of the trailer.
If you intend on having a Show Trailer, then you will want to keep everything original. This means a lot of "re" work. Paint would have to be done as original; you will be able to find the original type paint with a little effort. Pitted light fixtures can be either recoated or, if the pitting is not too bad you might just polish them up as best you can.
Most people fall into the "I'd like to keep it looking original" category and that means doing as in my 1st paragraph. Others fall into an "It's mine and I'm going to use it" Category and this means a highly personalized camper.
My preference it to keep it looking original, but at the same time remember that I am going to be using it as a camper.
Just adding my 2¢ worth
1975 31ft Sovereign International
........Rear Bath Double Bed Model
Tow Vehicle:1999 GMC Serria SLE Classic 1500 5.7Ltr
System: Jordon 2020 Ultima Brake Controller
Hook-Up: Equalizing Hitch and Sway Bar