Hello everyone, and especially Anonymous in post #11
To be honest, I have been surprised by the strength of everyone's responses here.
Anon: What you said made me realize that I do not see the leader of this dojo as my Sensei, and haven't for a long time. In retrospect, there was a real break around the time of my sho dan test, in which it became abundantly clear that he did not care about my progress as a student. There are, however, other teachers who do care about my progress, and because of my debt to them, and to aikido in general, quitting the art is not really right. Last fall, one of these other teachers said that I had put too much time and effort into aikido to quit now, and that I couldn't let this one person (never mind that it's the whole dojo culture!) take away my practice.
So, what I can do, living and practicing here, is to give up on the dojo, in a way, and just focus on my own practice - forget about teaching, forget about trying to bring people into the dojo, forget about trying to motivate everyone to go to seminars (well, except from a self-interested point of view in terms of carpooling), and, in short, be a lot more selfish about my practice and stop feeling bad about my refusal to practice with the (sometimes) angry guy, who the sensei clearly prefers over me.
I would like to see another dojo in this area. I think there are enough potential aikidoka around here to support two dojos . In the meantime, I may have to make a temporary move somewhere else so that I can practice regularly with a teacher I respect more.