Hi Erinna and Locutus.
I'm trying to get a handle on NMM at the moment also. Some of the above look like good efforts to me. Although I've found my own photos to be quite deceptive. The shoulder pad edging ones in particular look very nice.
What I have learned in my quest to make this happen in my own painting is that contrast is the key whether it is gold or silver or steeel or what ever you are after. That is why the shoulder edging in the above is close to working but the gun, the knee pads and the shoulder emblem are not yet. You need to push the darker colours darker still and probably include some spot white and some lighter highlights.
Also the blends between colours are a bit harsh at the moment. The best being the shoulder pad edges in the last two photos. Some glazes of he mid tone over the transition or of mix of the two colours involved would soften these up.
Oh and I've stuck a link in my sig to my blog.
Edit: oops forgot to enable my sig.
My stuff is here (what little there is for the moment).
http://www.coolminiornot.com/forums/showthread.php?38901-Stew-s-WIP-Log
Edit 2:
I just had another look at these on a better monitor (didn't know there was so much difference between the two). I think the colours in the shoulder pad edges are fine (maybe a little darker for the darkest). They need to be smoothly blended and they will start to look better. The emblem and the gun need the darker areas darkened quite a bit and smoother blending.