Lol,--- I, for one, adamantly discourage the "urban myth" of "gloss-decal-gloss". All that glossin' in just plain unnecessary--I say this because I regularly put my decals on without a gloss coat, and if I do, I simply "spot gloss" and then use a similar spot-coat of flat over the decal to seal it and provide a similar surface to the overall paint. I just can't see covering the entire model in a heavy coat of gloss when you only need it under the decals, I feel that the more clear layers you put over your paint, the more it is going to build up around small details--especially if you use a heavy "rattle-can" spray overall--and in the case of gloss, it dramatically darkens your base coat because of the nature of what gloss does to the diffusion of light. Try it, you'll see--gloss darkens paint--or at least your perception of it, which can lead you to misjudge your weathering efforts.
You can also "melt" your decals in to the paint with careful application of decal solution, and press a water-soaked soft brush over the decal to then press the decal into the paint while the water also serves to arrest the melting action of the solution. It takes a little practice, but I do that method 80% of the time. And don't forget--the closer you cut your decal, the less film you have, and the less possibility of the dreaded "silvering".
In terms of washes, I guess it makes sense to apply washes over gloss IF---and a BIG "if"!--you only want your washes to run off of the surface and collect in the creases; that IS, in fact, the "classic" recommendation for applying washes. However, in the style of "heavy weathering", I almost always apply my washes over a flat finish--or at the very least, a semi-gloss. This "traps" some of the pigment in the base coat, and acts like a filter at the same time, and "ages" the vehicle at the same time.
What Spamicus said though is true, too---don't try to apply pigments over gloss. They just won't stick.