The Trickster's Consort

[Eruanna]

Because of this, now I think Goldberry has something to do with Uinen, whose hair is spread throughout the waters of Middle-earth.

An interesting idea! Perhaps it gives credence to the theory that Tom and Goldberry are, in fact, Maia. Goldberry may have been in the service of Uinen.

I had always discounted this idea before, mainly because the others (ie Gandalf) were clearly affected by the ring, yet Tom wasn't and he could see those that the Ring made invisible.The Ring has no power over him.
Tom and Goldberry seem to belong in their environment, they are very much part of the fabric of the land and the seasons, and yet apart from it.
To paraphrase Goldberry, they are.

Elemental spirits is the closest description that I can come up with, yet that does not solve the enigma. I hope that far more erudite posters that I may come up with something better.