I agree that the scheme is currently too "flat" (in depth, not sheen), an issue which is more likely with a "plain" scheme like this one. Picking up on some of your suggestions, I am considering:
1) Paint chipping. This would include chipping on major panel fasteners around the nose, and chipping around hatches or elsewhere. I lack detailed WWII-era pictures showing the "elsewhere"; any suggestions? I would be willing to purchase a book or 2, if someone knows of one with good large-scale images from WWII (color a bonus). I am not sure how realistic the "highlight all panel lines" approach used in some of our existing skins is, even though it does give more depth.
2) Liquid spills; limited photo coverage of this, but have 1 good picture of bottom of plane in flight showing what appears to be oil leaks from numerous places.
3) Some additional variation in the green/grey "paint", either in the form of a few replaced panels, repair overpainting, or some sort of panel color variation from weathering. I would need better real photos for this though; see book request above.
4) Conventional 3-d effects, such as slight shading on forward edge of aelerons/elevators, and darker panel lines where frequently removed. My limited photo collection may be barely adequate as reference for this.
5) Less conventional 3-d effects; note the subtle highlights/shadows at the edges of some of the panels on the following image. Would seem to require "1-sided" gaussian blur in black on shadow side and in white on sun side of panels. Haven't thought of a good way to do this in Photoshop yet. I could do regular gaussian blur and erase one side, but that is mindlessly time intensive.).
