Funny you should call them "stumbling caps." I think of the initial capitals more as steps ascending a grand staircase. After the end of the line before, and the emphasis given its last word by the rime, you have a new word stressed with the cap, signalling the reader to lift it up a bit. When lower cased, it's like running down a regular flight of stairs.
I suppose with that metaphor, the stanza breaks are like landings in between the steps. There's usually nothing there but space, to either pause for or leap over, depending on what the sentence and sense is doing, but occassionally, there's a peculiar ornament on the landing, as in Coleridge's
Rime of the Ancient Mariner . Here a swatch from section III:
At its nearer approach, it seemeth him to be a ship ; and at a dear ransom he freeth his speech from the bonds of thirst.
With throats unslaked, with black lips baked,
We could nor laugh nor wail ;
Through utter drought all dumb we stood !
I bit my arm, I sucked the blood,
And cried, A sail ! a sail !
A flash of joy ;
With throats unslaked, with black lips baked,
Agape they heard me call :
Gramercy ! they for joy did grin,
And all at once their breath drew in,
As they were drinking all.
And horror follows. For can it be a ship that comes onward without wind or tide ?
See ! see ! (I cried) she tacks no more !
Hither to work us weal ;
Without a breeze, without a tide,
She steadies with upright keel !
The western wave was all a-flame.
The day was well nigh done !
Almost upon the western wave
Rested the broad bright Sun ;
When that strange shape drove suddenly
Betwixt us and the Sun.
It seemeth him but the skeleton of a ship.
And straight the Sun was flecked with bars,
(Heaven's Mother send us grace !)
As if through a dungeon-grate he peered
With broad and burning face.
And its ribs are seen as bars on the face of the setting Sun.
Alas ! (thought I, and my heart beat loud)
How fast she nears and nears !
Are those her sails that glance in the Sun,
Like restless gossameres ?
The Spectre-Woman and her Death-mate, and no other on board the skeleton ship.
And those her ribs through which the Sun
Did peer, as through a grate ?
And is that Woman all her crew ?
Is that a DEATH ? and are there two ?
Is DEATH that woman's mate ?
Like vessel, like crew !
Her lips were red, her looks were free,
Her locks were yellow as gold :
Her skin was as white as leprosy,
The Night-mare LIFE-IN-DEATH was she,
Who thicks man's blood with cold.
Death and Life-in-Death have diced for the ship's crew, and she (the latter) winneth the ancient Mariner.
The naked hulk alongside came,
And the twain were casting dice ;
`The game is done ! I've won ! I've won !'
Quoth she, and whistles thrice.
Or, with the room and corridor metaphor, Coleridge's Victorian stanza headings or side notes (depending on how the book is typeset), are like paintings hung in the hallway.
The interesting thing here is that the placement of these accomplishes the same thing as a novelist does with the placement of speaking verbs and inter-dialogue action: It controls the space of the pause between speeches.
For example, take the four following examples:
"Your book? Oh, it's here somewhere." She glanced around the room.
"Your book?" She glanced around the room. "Oh, it's here somewhere."
"Your book? Oh," she said, glancing around the room, "it's here somewhere."
"Your book?" she said. "Oh," She glanced around the room, "it's here somewhere."
Basically, the brain reads the dialogue in a string. When there's a pause for exposition, the brain times the pause of the character speaking to the interval that it take the reader to read the exposition.
With narrative verse, Coleridge is doing the same thing with his headers, timing the interval of the dramatic pause to create either startlement with the short clipped four-monosyllabic-word headers, or else suspense and dramatic tension with the longer descriptions.
The varying length of the stanzas and the grouping of differing numbers of stanzas under headers also lends to this effect, as well as helping in some ways to mimick the feeling of a sea voyage.