PianoMonk So... once a musician has a piece "worked up" it's not possible for them to learn anything more about it? Have you ever actually worked with other musicians in a recording session? Improvising over, let's say, a 2 - 5 - 1 section of a song using various scales or modes, and working on which of those is best suited to what one wants to convey, is most certainly, in my humble opinion, a learning exercise.
Wading in here - what I'll write may make sense or no sense.
What I learned predates Molly Gebrian's recently discovered material by 15-20 years from where I began. I am not following what she presents as such. Her ideas mesh with some of the things I learned, but there's less. The goals I've seen so far also seem to differ at times. She seems to be looking at what she needs at this time for what she herself is doing and applied in a manner that suits her needs. (Discussed recently somewhere here - hence her encouragement to tweak for your own needs).
Ok, so when I work on music, I may apply things I know to shape the piece. In a "classical" context where you're not changing notes or find better chords, you might choose to stress or bring out this or that note, put rubato over here in this way, do this or that with the pedal. You may want to coordinate something between your hands and feet. You're using what you have and know, like an internal dictionary that you possess. What you describe seems a non-classical application, and here you must possess a dictionary of chords, progressions, scale types - whatnot. As you develop things you are learning, keeping what works, discovering things. Maybe I see this as a kind of free-flow. I've done my variant of that and the clock stops. Suddenly its an hour later and you don't know how that happened.
There's another kind where I'm forming that dictionary. A lot of it is also like I'm playing "from the surface of my mind" without that deep an awareness. I have had to learn to hear not just when a note starts, but also when it ends and flows into the next note. When I play a melodic line that seems predictable, am I actually hearing it or am I inserting a note that seems right but isn't that note? My way of pedaling was to press way down and lift way up, because of my first poorish instrument. To change that around needed inordinate, moment-by-moment concentration. Any moment I thought I was still doing it, but had gone into freeflow. For THIS kind of learning and focus, that only lasts a short time.
I think we have different kinds of learning, different kinds of practising, different kinds of goals. Might that make sense?