@mpechner, I played around a bit and I see your point. The Adafruit library files are actually supposed to be kept together. I think the way the library feature is done right now is they have to be self-standing so they cannot refer to one another. You should add your comments to the library topic:
BTW, I will be publishing my mfGFX library soon which includes support for multiple, user-defined fonts. Given the structure of the Spark libraries, I was looking at including different displays as examples but I am not sure if that will work as intended. So stay tuned 