This is an AMAZING discussion with so much insight, wow.
I really can't add much to what has been offered as suggestions but just wanted to chime in that this topic is critical. It is nice that so many of us work very hard on these challenges.
I start this thought-process at the compositional stage and revise my delivery on through the presentation stage, this is primarily why I rehearse so much. Getting the flow and interest retention 'schematic' just right takes me a lot of refining time.
I think it is cool how many loopers are considerate of the non-musical audience member with short attention spans. When I am alone in the studio, I can go for hours working out the parts and changes of a piece but on stage, it is all about melodic priorities, duration efficiency, tonal variety, interesting content and changes, etc.
Great topic and wonderful responses!