I coat my models with Klear as this seals the paint and decals. Then I apply weathering and/or other coats on top. I often apply a mattcote first, as this allows the weathering powders to adhere better and also dulls down the glossy decals, then if I think the overall model looks too flat, I'll seal again with klear. I think a satin effect looks just the job, especially on fabric surfaces. Wood, metal - they can get away with being glossier. An overall gloss effect would be too toy like in the small scales, in my opinion.
All the (few, mainly British) WWI aircraft I have seen in museums have what I would describe as somewhere between matt and satin, although are clean and reproduction/repainted. The areas where the fabric is stretched more, ie over wing ribs, appears more glossy. So in my method above, I would use klear to get a glossy coat first, then mask the ribs etc before applying weathering and mattcote - this is a method I need to practice but I have seen some excellent finishes on here from others