What are your settings ( in your MR render globals ) for your min and max radius in your final gather tab, and also your final gather rays? Increasing those settings will give you a cleaner render.

Very cool color maps. I have never seen a epidermal map before. I have seen many subsurface maps, and diffuse maps, but not epidermal maps. The dryness look could be from the epidermal map, but I'm probably wrong on that. You mentioned using negative lights. I have never seen anyone use negative lighting on a human model before. Try lighting with normal values on her and see what she looks like.

Finially, if your willing, send me the model and let me do some test lighting on it. I can send you the results outside the board so that it does not interfere with the challenge. But this is entirely up to you.