Welp, one step forward, then two back...
As of Friday, AudioWagon permissions were sticking throughout the day, I didn't have to keep giving it permissions on each car start, but no longer - back to requiring permissions.
For google maps navigation, changing the prompt volume during the response to a "Hey google, navigate to..." command (where it says "navigating to...") works, does persist, but it no longer gives the spoken directions. I went back in under the main Settings - Sound, to check, nothing obvious to change. It is navigating, the directions are showing on both the center and panoramic displays, just no audio directions
I'll play with it a bit more, but shrug...