Hello Gunnar,
Although I have only been actively visiting the US Archives at NARA II in College Park for about four years, as far as I know, the US archives have always been open to the public. I don't understand how any one person can prevent access to WWI records. I do know that trying to get material from the archives is difficult if you can't visit it personnally and search for what you want. One reason for this is that the primary job of the archive's employees to maintain and preserve the records, not serve as researchers for the public. Therefore, depending on who you contact at the archives, the level of assistance varies. It also seems that as the older, more experienced archvists are retiring, the knowledge of the various collections among the archivists is decreasing. That leaves people who live far away from the archives little choice but to either go to the archives themselves (which can be expensive and time consuimng) or to hire a professional researcher (which can be good or bad depending on the researcher).
I go to the archives on a routine basis - about one a week. I have not been denied access to anything except the rarest and most fragile of documents and photographs. It is, however, time consuming to find and search through boxes and boxes of materials and then copy them. For this reason, I sometimes help other people with small research jobs, but even then, I have to limit it because research is time consuming and I have my own work to do (I scan and sell digitzed copies of WWI and WWII documents and photos).
I have seen a few German avaition records in the WWI records - mainly information about Allied bombing attacks and a flyer casuality document. There is also a nice collection of official German photos. If there is something simple I can help you with, I will try.