Poetry in The Hobbit is definitely front-loaded, 12 of 17 come before the beginning of Chapter 10.  Hmmm.  My expectations about higher register after 10.020 did not predict that, because I immediately associate “poetry” with “high register”.  Let’s examine them more closely:

01.063: Chip the Glasses
01.072: Far Over the Misty Mountains Cold
01.142: Far Over the Misty Mountains Cold (reprise)
03.014: Tra-la-la-lally
04.019: Clap! Snap! the black crack!
05.026 through 05.063: Riddles
06.074: A Horrible Song
07.099: The Dwarves’ Wind Song
08.096: Attercop!
08.100: Lazy Lob and crazy Cob
09.049: Wood-Elves’ Barrel Rolling Song
09.053: Song round the River-Door
10.035: Snatches of Old Songs
15.036: Music to Soften Thorin’s Mood
19.002: Tra-la-la-lally Refrain
19.011: A Song Loud and Clear on the Banks of the Stream
19.029: Roads Go Ever On and On

I would submit that poetry in chapter ten and after is all heroic, nostalgic, high-register poetry except for the 19.002 Tra-la-la-lally refrain.  But what about the Tra-la-la-lally refrain?  Is it, in fact, as silly and light as we observed the earlier, 3.014 Tra-la-la-lally?  I suggest that it is not.  Our singers go nowhere near “Tra-la” in their song until after the dragon is withered and his splendour is humbled.  We get rusted swords, perished thrones, and trusted strength betrayed.  Only then do we hear that grass is still growing, that nature can be in its proper order, and the weary traveler is welcomed back to The Last Homely House.

The 19.002 Tra-la-la-lally Refrain heals.  It is the closing parenthesis on Bilbo’s experience of war, an invitation to encapsulate the pain and fear and reach a landmark in his return to wholeness.  “Stand down, little fellow who has gone to war.  The world you knew is shifting back into its place, wider of margin and more precious for its cost.”  I place this poem firmly in “high purpose” although the familiar words of the refrain may be of silly register.