as a 3rd kyu with no special abilities and a slow learning rhythm I read through this and come to the conviction that I would certainly be one of the persons whose attendance at high level seminars would not really be desirable. I have all the defaults George Sensei observed. The last seminar to which I participated was with Osawa Sensei, and I am not so dumb that I don't see that I was in most of the cases NOT able to replicate what he showed us but was stuck in repeating what I knew from my dojo. The seminar was about the basics, just doing the basic movements and showing us some new approaches that could change them slightly to make them much more efficient.
At the seminar there were LOTS of people like myself, and he did NOT get angry with us. He came around and tried to correct individually each of us...quite patiently and sometimes successfully (not with myself...I didn't get that particular technique
notwithstanding special teacher care). Maybe he knows that we were just trying our best, but this "best" is limited for many people.
Here in Belgium, if there is a seminar with a great shihan (not only Japanese! If Tissier comes, it's the same, and certainly a high level American would be equally appreciated), you have easily 200 - 300 people on the mat. Many of our local teachers, among whom we also have a good number of 6th and 7th dan, assist, but obviously the largest number are lower dan and all sorts of kyu grades. But there are also some master classes (like "only for dojo cho" or "only for yudansha") in Belgium, but these are something like 2 - 3 per year.
I never had the impression we, the lower grades, were not welcome, or that our low proficiency level was considered as an insult to the teacher. As a relative beginner, I think even people at my level can learn lots of things at the seminars, although we cannot pick up everything the teacher shows and are often stuck with our own ways. And it gives us an idea of the greatness of aikido, the difference of styles, approaches, possibilities etc. We get out of our dojos' routines, and we can see where we might get one day if we practice hard and well. But how could we practice more and better in order to get a technique we are doing wrong if no one shows or explains us? We would just repeat our errors.
So, maybe from the point of high level aikidoka it is not so nice to have a lot of beginners swirling around during a good seminar, but still for us it is a necessary experience we are getting something out, be it limited, and I think we should be encouraged to go to those seminars.