[Morthoron]

From my standpoint, Goldberry (and her fashion-addled hubby, Tom) are enigmatic because they do not fit in a cosmogonical sense in Middle-earth -- they are in fact from outside of that universe. They do not precisely fit categorically into any designation in Middle-earth (they have attributes of Maiar, but have puzzling disparities as well); this is, I believe, Tolkien's personal joke on all of us.

When Bombadil (and by extension, Goldberry) claims he is 'the first', that is Tolkien winking at us, because Tom's tale did indeed come before the writing of LotR from both a conceptual and published standpoint. Goldberry and Tom, by Tolkien's own accounts, were important in their own right as characters and warranted their inclusion in the LotR. In fact, there is a letter Tolkien wrote to his publisher asking if Tom might be included in the story, although he does not necessarily fit tidily. Tom (and Goldberry) were written in for no other reason than Tolkien liked them and thought they were important in a personal sense beyond the telling of LotR.

And thus, like balrogs wings, the intellectual battle over Tom (and Goldberry) rages on unabated.

P.S. The Maiaric reference to Tom and Goldberry are certainly strong, particularly the maintenance of power in a defined area (much like Melian's girdle), their affinity and reverence of woods and water (like Maiaric disciples of Yavanna and Ulmo), and their power over the unseen (spiritually -- as in the Barrows) and nature (physically -- as in Tom's taming of Old Man Willow and Goldberry's washing day).