It seems to me, that a strong structural purpose of the Tom Bombadil ‘interlude’ is to provide a reason why the Nine Riders don’t get hold of the Hobbits very quickly. The 9 were closing in fast, the Hobbits really don’t have the capacity to avoid the 9, and so they have to ‘disappear’, have to become impossible to track, so that the Hobbits can then emerge so close to the Prancing Pony Inn that they can get there before the 9 can catch them.

After knowing that you need to ‘hide’ the Hobbits (because you made the 9 close in too fast because you wanted to increase the tension), the rest of the Bombadil and Barrow material is just trying to make something happen while the Hobbits are hidden; something that adds a bit to what the Hobbits need (proper weapons; small bit of info) and to add thematic bits to the overall storyline AND perhaps, as an afterthought, to give the reader a sense of hope– in that the Ring, while very very very powerful, is NOT the end-all, be-all.

Just my two cents.