Just one point to make.
David - you have hit the nail squarely on the head regarding what this thread is about. Your thoughts were formulated so well that my own thoughts started taking on a more coherent and structured fashion.
Your concept on seminars is very interesting and makes great sense. Often when I travel and visit Aikido dojos the measure I get of an Instructor's skill level is gauged pretty much entirely on his technical skill in cooperative practice or demonstration, which is a good thing, but often the Instructor's real knowledge and application of sound technique and spontaneous Aiki is a different thing entirely, as you indicated previously with your experience. I often wonder if many of these Instructors can execute the same quality of technique on someone from the crowd who is not a member of his dojo or not his official Uke during seminars. In other words, does the Instructor embody his technical knowledge to the point where it really does not matter who the attacker is, how tense, spontaneous or resistant he is, so the result is still the same every time the technique is done. I know there are a few Daito Ryu teachers (Takeda's direct students) who could do this to pretty much anyone.
In Aikido however I get this feeling that people assume that if the Instructor does not have his official Uke that his performance will be somewhat compromised (this does not refer to a demo which is something else, but during Instruction) and often any mishap or mistake is seen as the Uke's fault. Though this may be true for folks with poor ukemi skills, for those who can take the ukemi, what is the reason for this discrepancy in execution between someone familiar with the Instructor's movements and someone who will simply only take ukemi when actually thrown?
To me it reflects well on an Instructor when he has a degree of faith in his abilities to do seminars or visit dojos without necessarily needing a personal Uke, but being fully capable of executing technique and manifesting Aiki on pretty much anyone who takes part in the Instruction, regardless of how much that person may not respond in a "typical" manner.
Just some more thoughts.