I love this kind of visualization.
I once mapped out all the colours mentioned chronologically in James Joyce’s Portrait Of The Artist As A Young Man, which corresponded in an interesting way (to me) with the narrative developments. I even tried to create paintings for each page of the colours (something like your heat maps), but that was before such things were as easy to produce as they are now, so I abandoned it as a bit too abstract a task. Besides, I reasoned, the colours are words in the text, so why not leave them that way, especially given the range of hues seen by anybody in their mind when reading it. You may have inspired me to try it again, however, just for fun.
One further note, Gertrude Stein saw commas and most other punctuation as unnecessary, and Kerouac too abandoned use of them often, so I wonder how their texts would look mapped according to your method.