Hookbill, what I think (and looking at my post it wasn't really clear) is that Old Man Willow is more of a tree who has grown Entish. He can't move about as an Ent would, but he does have some of the intelligence or cunning of an Ent.
I know what you mean about Old Man Willow being a central point to the air of malice in the Old Forest, as though he is an influence on the other trees. So, here's one person who certainly thinks you've no need to eat tree-roots!
Davem, now I'll have to go and read Adventures of Tom Bombadil again! It's just struck me that Goldberry is rather like Ginny Greenteeth, the weed that floats on slow moving rivers and brooks, and which is supposed to be a female water spirit who drags the unwary under (this folk story is a very vivid childhood memory, probably told to me to make sure I stayed away from waterweed).