Frankly, I would think that is too much for a 1959
in "great shape". If you were so amazed at the condition that you described it as museum quality original, incredible how intact it is, stored indoors to prevent UV damage, then I would ask 30k. But in "great shape" I would go closer to 25k as an asking price, and I wouldn't necessarily bet on getting it.
It all depends on how much time you have. The market for people who want "original quality" Airstreams is small compared to the market of renovators, remodelers, and small business (food truck, etc.) owners. They all want to gut the interior and rebuild.
But if you have plenty of time to sell it, ask $30k, that way you can hope to eventually find that perfect buyer who is looking for the original quality trailer.
Just what I learned from our search, but my background isn't worth much compared to some of the much more knowledgable people on here. Good luck!