I'm from one of the two dojo's that arranged this years Nishio-camp in Denmark. I'm really glad you liked it and like you I hope, that Nishio Sensei will be able to appear next year.
I am probably not the right person to explain Nishio Sensei's behaviour, but I will try to give my interpretation of some of the things he said, that could sound a bit harsh.
You wrote: "Nishio Sensei doesn't seem to have a particularly high opinion of other peoples Aikido." and I agree that you could get that impression. However Nishio Sensei has been getting a little old lately, and I think he is concerned that he might not be able to come back, and therefore it becomes more and more important to him to get his idears and thoughts across before it is to late. Another aspect of his age is, that he can say that kind of things and get away with it by using an 'I'm just an old man' attitude as a 'cover'. On top of this one must remeber that Nishio Sensei became a Shihan very fast compared to other Shihans of his time, which made it very hard for his sempais to figure out how to place him. In a way he was below them due to his fewer years of practice, yet his grading and title raised him to the level of the other shihans. I suspect that this led to Nisihio Sensei being looked down upon in some situations, but by now he has build up a confidence in his aikido (50 years of practice does indicate some sort of authority) so he speaks his mind openly. I also want to point out that many of his comments where an attack against the tyrani of tradition. He often said "In other dojo's they have done it this way for many years, but I changed my way of doing it." I think that shows, that even though he is an acomplished Aikido-ka, and even though he is in his 70's he is not afraid to let his aikido develop further, and change it when he finds 'weak spots'. I don't know what true aikido is, but I strongly believe that this ability to develop your personal aikido is a large part of it. Personally I like his openhearted comments. It is refreshing to meet a japanese person who dares to speak his mind and take a stand even though it might be against what is concidered good manners. Don't judge him too harshly - just enjoy his wonderful teachings and extract as much as possible from this source of knowledge before it dissapears for ever.
Please excuse my ramblings. Se you next year in Saeby in North Jutland