In other words, I don't anticipate ever accessing a master directly. When I want to work with an image in an app outside of LR, I'll just export a full-size .jpeg.
This makes perfect sense to me.
Your masters can be anywhere you want them to be. Lightroom doesn't care, it will work fine, and if your philosophy is as quoted above, then you shouldn't care either. You have a perfectly workable system for finding your photos.
dj_paige is entirely correct (as he always Is), but I would add one caveat. SOMEDAY you will want to move ALL your masters to another drive (think new computer or bigger, faster, better HD), and then it will be very much easier to have all the photos in one file for both moving and perhaps reconnection to the LR catalog.
then it will be very much easier to have all the photos in one file folder for both moving and perhaps reconnection to the LR catalog.
Yes, that's a good point, but it could be a few folders rather than one folder. But the main point is that you can put your photos anywhere you want.
Would there be any benefit to engaging in the cumbersome task of relocating that mobile masters to the same folders my CC images are in?
Is Mobile's default location covered by your normal backup procedures? If not, maybe move them to a part of your system that is included.
What will happen if you change computer? Will you remember to migrate these default folders?
For me, these are just two questions that make me nervous of leaving photos in the default mobile folders. These are originals, even if they're not shot on a proper camera, and I prefer to keep all my originals in one place, So I do move them.