Generally agree with most of the points made - in fact many are the the same points made concerning politeness I learned while growing up.
However, you can be well mannered and polite, you can also use the correct manners and be extremely impolite. Intention on the part of the other person means far much more to me than having the correct "form" in your actions, so I often do find the aikido adherence to various bits of Japanese etiquette (which varies widely dojo to dojo) is rather silly and annoying, but not really a major issue apart from the seiza business.
Etiquette in the dojo is like any other form of manners, it's there to smooth the bumps of human interaction and maintain the correct behavioral code - but the overriding importance to me for dojo etiquette is it should provide the correct amount of discipline necessary for everyone to practice safely. If it's not involved with safety, I really don't give it too much thought (but my mother claims I was never polite)
... think you will notice if you look that the quality of the reigi before a performance or enbu of any kind is indicative of the quality of the rest.
This I will probably disagree with if I was certain about what "quality" we were discussing. If you're referring to the quality of a demonstration in terms of it's choreography, I could agree. If you're talking about martial or technical proficiency, I have to disagree - I've seen some scruffy shufflers wander on to the mat and be rather amazing to watch.