Not to downplay your search, but when it comes right down to it, a snake is a snake is a snake.
I cannot, in right contemplation, suggest you further your search for western serpent knowledge. (Hermes and Genisis and such)
The understanding you're finding is mostly Western based and yes, very dichotmous...the good/bad thing always kinda gets under my skin.
There is a wisdom there, for which I usually contemplate the Egyptian Goddess Selkhet (same poison...different form) and in India, the snake is held by several deities as a "transformer of poisons"
http://www.boloji.com/hinduism/127.htm
It is there that I suggest you continue your quest. Western thought kind of clouds the mind and puts forth the idea of "knowing" instead of "wisdom"
Good luck,
Thet