I respect your opinion Daniel, even in disagreement. Let me touch on a couple of points you brought up;
It isn't that the attire isn't important, but that it is the appropriate attire for the environment.
It isn't appropriate for the environment out of necessity, but of what has come to be expected. Referencing the book that both I and Glenn have quoted from, one can see Uechi Kannei Sensei (and senior students) in the short pants (akin to a type of adult diaper worn there because of the hot climate) on pages 10, 11, 12 and others. We can see just the bottoms in more pages than I can list. Most of the kata demonstrations by Uechi Kannei Sensei are in just the pants. In fact, you only see him in full uniform and belt in a few photos throughout the entire book and those are photo op pictures and not training pictures. Sanchin kata is never trained in full uniform, particularly when it is part of the promotional testing portion. He was far more senior than anyone in the Korean arts, the same with all of Uechi Kanbun Senei's senior students. This is how they trained on a regular basis.
GM Dunn, who originally received his first BB on Okinawa rarely wears a uniform and belt. At our annual seminar coming up it is a running joke among those of us in the TAC if he'll be wearing one
The bottom line is that it is a nicety, but by no means a necessity.
Mastercole also explicitly said why; he felt that if they dropped the uniform that it signaled other potential problems, not that the uniform itself was a priority.
This is an opinion, not fact. Not wearing a particular outfit in no way, shape or form indicates the level of the training. As evident from my commentary on Uechi Ryu and the seniors in that art (and others to be sure), they rarely wore a full uniform and that philosophy was passed down to others that became seniors. Rather than 'signaling other potential problems' as he surmises, it may signal a move that training is priority and uniforms and rank symbols aren't. It may signal that one's skill is directly related to what they can do and teach rather than what is on their waist or what type of uniform (if any) is worn.
Not patting myself on the back (so it should not be taken as such please), when I had a commercial school I had students coming from the surrounding four counties to receive training with me. I very rarely wore a uniform, the same with them. We trained exactly as I have described in various threads such as my Self-defense Training Methodology. These included high liability professionals as well as private citizens. They were there for what I offered, not for what they could wear. Now that I teach privately, I still don't wear a uniform and I have to actually turn down new students due to lack of time. I offer to put them on a waiting list and they accept. To me, and this is my own personal/professional opinion and no offense intended to anyone, that is proper training mind set. If one needs a particular uniform and a particular belt to be able to train then they are there for entirely the wrong reason.
Of all the people that I taught while not wearing a uniform...no one ever had to wonder who the 'Sensei' was in the school. When a new student walked into the school, they never wondered who the Sensei was or the level of skill the other students had. It was evident by watching them train.