Personally, I think
Bombadil is
extremely important to
The Lord of the Rings. Not in an obvious way, but I think
Tolkien put him in there to state his admiration for pacifism, even though Tolkien was not a pacifist since he viewed it as unfortunately impractical.
As to who Bombadil
is - that's a very interesting question. Personally I think
Goldberry is an elf-maiden, probably one of the
Nandor. Though the poem in The Adventures of
Tom Bombadil states she used to live underwater, personally I think by the time Tolkien wrote LOTR, he pictured her as merely living by the water. The fact she was interested that
Frodo is called 'elf-friend' imo implies strongly she is an
Elf.
Bombadil on the other hand, is much more complex. I think he is an Ainu, but not a
Vala nor a
Maia. I think he is un-affiliated with the
Valar, at least directly, that is, he doesn't serve any of them. I think he was the first being created by
Eru, and also
the one that is the most free from
evil and in mind closest to Him.