Let me attempt to set your mind at ease.
1. Say the following sentence out loud. The use of the word trailer is not bad. It is a trailer, but it is the best kind of trailer, because it is an AIRSTREAM.
2. Plan on using some elbow grease to simply pull the propane bottles and sand the A frame, treat it with some POR 15 to stop the rust, and them paint it silver again. This is a standard maintenence item.
3. The odd flex or bow you mentioned is more than likely just the way this one was put together. I looked in my "History of the Land Yacht" book and the new ones sitting in the factory have the same bow as you describe on some of them. One of the reasons that an Airstream lasts so long is because it flexes and springs back. I would watch the area, but don't lose any sleep over IMHO.
4. By 76 the rear end seperation issue from a design standpoint was addressed in manufacture. This is not to say that abuse and neglect could not cause it, but looking at the picture it looks great.
5. You are teasing us with the idea that you have many pictures of the trailer but only posted one. You have an album you can fill right here on the forum. Then we can all pour over them.
Welcome to the forum, we look forward to seeing more of your new prized posession.