The specularity file controls the strength of the reflections from the sun. For matt paint I usually have it set to a greyscale value (i.e black=0, white=255) of about 50 and for bare metal 100-130. The power map controls how focused those reflections are and for matt paint I use a grey value of about 25 and for bare metal 80-100. The environmental map controls the reflections from the landscape and sky and I set this to about 10 for matt paint and 70-100 for bare metal. My bare metal colour in the diffuse file is RGB 140/140/150 which is way darker than the colour I used to use for AHII skins.
Post lighting is not something that can be controlled by the skinner. You just have to make a decision whether to edit your skins so they look how you want with it turned on or off. Unfortunately its not possible to make your skin look the same for every player's settings, its always a compromise.