Gunter, Gruss Gott! (Sorry, don't know ho to make the double "s" with my keyboard.)
As we all know, fabric covered a/c of the time were covered with cellulose dope which imparts a glossy finish, therefore the a/c, when new, would be glossy also. However, if we painted a model such as a 1/72nd biplane and put a glossy finish on it, it would look toy-like. Look at modern a/c such as jet airliners or autos which carry glossy finishes, the farther you get away from them, the less glossy the finish looks to our eye. I have seen the scientific arguments to explain why this occurs, but I'd rather not type it out, and I don't think we need to go into it here, it is what it is. Maybe we can chalk it up to "scale effect". As for me and my house, I think using a "satin" finish of some sort works best when trying to replicate this effect. I completed a 1/72nd Fokker Tripe, and finished it off with a VERY light coat of Testors "satin". From normal viewing distances, you cannot see it, it looks flat, if you get very close, you can see the finish is not flat. I was satisfied with this effect. In my very humble opinion, I think you can up the degree of "satin" as you climb up in scale, but even in 1/32nd biplanes I think a true "gloss" coat should be avoided.
(FWIW, since you brought up NATO camo schemes on vehicles, etc. I remember when I was a mechanized infantryman and armor crewman in the 80's/early 90's, all of our vehicles had a "flat finish". It doesn't take long for that paint to go "flat" from sunlight, weather, etc.)
On another note, I also think we should stay away from heavy weathering. I've seen some modelers weather WWI a/c to make them look like flying dust bins/garbage cans that were serving in the North African desert or on a Pacific atoll exposed to all of the elements for weeks or months. During WWI, these a/c were cutting edge technology, and they were babied and sheltered as much as possible. Sure, you can find the occasional photo of an a/c looking extremely worn, and on its last legs, but look at the majority of images. Most show well maintained airframes with a little exhaust or staining from castor oil, etc. One
hardly ever sees very faded paint/dope, etc. except on airframes that are just worn out.
"Fabric Effect"? Don't even get me started.

Warren