weathering metal finishes without killing shine

The weathering process on real aircraft would remove the shine. In my humble opinion a natural metal finish that is to shiny looks toy like. Recently I have started giving NMFs a cote of Klear (Future) before weathering. I use artists oil paint for a wash, in the case of a NMF I use a dark grey. I am actually toying with the idea of giving my latest NMF finished model, a P47N Thunderbolt, a cote af matt, or more likely semi-matt varnish. You can see this model, at the wash stage, at the MSN picture site at Armorama. www.armorama.com
However if you want to keep your NMF shiny you would probably need a very controlled method of accentuating the panel lines (I'm guessing thats what you mean by weathering and retaining the shine), cos like I say a weathered aircraft would loos it's shine, to some degree. One method would be to use a draughtmans pen. the type with the very fine nibs. One make that springs to mind is Rotring. They come in different colours. I don't know if they will work on a shiny NMF though
Hope this helps.
Mal