I have never had the sense of any 'menace' coming from Goldberry. She does seem to flirt with him, though, in order to attract his attention. There is an old saying (or perhaps it's a song) that '
a boy chases a girl, until she catches him'
Tom, on the other hand, always seems to me to have an underlying power, a sense of danger. That perhaps he is not as innocent as he first appears.
This lack of children is an interesting point. Apart from human and hobbit children are any mentioned?
The ents are unable to reproduce because of the disappearance of their entwives. The elves seem to have had their children long ago and no 'new' offspring seem to be around. I remember reading that elves could delay reproduction in times of war/trouble; but is there something else here?
The elves, knowing that they will soon be gone, are no longer 'investing' themselves in Middle-earth, there is no future for them there.
The dwarves seem to have very few females. Although we have
'son of...'etc, they are all adults and no actual children are mentioned.
Tom and Goldberry have 'retired' into their own little world of the forest and surrounding area. Perhaps, as
Lalwendė says, representing nature, they have no need to reproduce. There is also the question that being immortal there is no urge to 'leave behind' a family for posterity, but then that theory doesn't work for the elves.
Are the older races of Middle-earth heading for eventual extinction? Is it truly Man's time? If that is so then Middle-earth will be the poorer for it.