I might worry about over specializing as well. When there are too many elements you get parts of the system that people will gloss over entirely and then there's just no reason for them (I'm looking at you, Fog). I like the concept though, very cool.
One of the things I've always loved about the traditional Chinese five elements is that each one has an emotional and biological association (for example wood is associated with anger, patience and charity, as well as the liver, eyes and gall bladder). Makes for a really interesting element system where at least from a neuromancy/biomancy standpoint each element is unique in what it can do.
Why do hotdogs come in packages of 10 and hotdog buns in packages of 8?
Because Bratwurst come in packages of six.