Hi Rob, we know so little about "pagan" or rather ancient religions that it is difficult to conclude about what they meant by the serpent in my opinion. Unless we exclusively consider the pagan craze that had place just before Christianity, the human sacrifices, the orgies, black magic and other excesses. But what were the beliefs thousands years earlier? Ancient Egyptians had lots of different snakes/serpents. There was a Kundalini-like ureaus protruding from every Pharaoh's brow: a sign of illumination. There was Apopis: a monster serpent that was lurking and waiting to swallow the Sun god and thus create Chaos forever. The priests ritually slew the symbol of this beast every day.
Also: the ancient Egyptians had a notion of the "hidden" god Amen/Amun:
“Three gods are all the gods (are one): Amun, Ra, Ptah, who have no equal."
Obviously then, we can't say that the serpent was equal or superior to this god. So you see, perhaps the beliefs have dangerously degenerated later on but I feel there was a lot of wisdom (more so scientific and spiritual than "religious") in earlier antiquity, all encapsulated in symbols that we can't even understand today. This is so frustrating! I know intuitively that the Jewish scriptures contain similar wisdom, but apart from tiny glimpses like the Ezekiel Wheel we are still blind to the whole spectrum unfortunately.