You know, I'm not sure what you do for a living, but if you aren't a professional illustrator, that's a damn shame.
Well, I am getting paid for some of my work these days but I sure would love to be doing it full-time.
Seems like you've got a pretty decent handle on that already in the areas you've put more time into. One thing that should help, if you weren't already planning to, is doing your final pass without transparency and layer effects and other purely digital tool. Just high (if not 100%) brushes (perhaps with some fancy brush dynamics on) and a little smudging here and there. It is a challenge but it does force you to use more physical medium technique which in my experience lends it more of that physical medium look. Either way it is looking great.
As I continue refining details the texture overlays should gradually disappear or get painted over. I'm just using them right now to add some texture to the piece. I'm not using any layer effects at all other than blending modes.