Have Elf, Will Travel

[Dininziliel]

Saucepan Man--points taken about Sam and Bilbo. I think it's still debatable, but is definitely more illuminated now!
SM:

Elves had enough flaws to give the Ring something to work on.

This is a good point. Which is why I think the question that ended your post is a good one--

SM:

Which leaves the question of why Tolkien does portray Frodo as having these Elvish qualities, which become more apparent as the Quest unfolds.

I wonder (wildly) if Tolkien was not trying to reconcile the Elves' "karmic" debt for their deeds in The Silmarillion?

Then there is this idea posted by tar-ancalime:

all five major-character hobbits develop special relationships with other races,

This is in keeping w/what originally piqued my curiosity. It is also another thing I had never noticed--the hobbits as a combined group seem to serve as a moving reflection of and a reciprocal influence on all other free peoples they meet in ME, or something else that I can't quite put a finger on.