How would you teach them to new students while also trying to keep their interest in aikido fresh? How do you rehabilitate a more seasoned practitioner to look for the principle rather than focus on the wasa?
I know George can speak for himself, and I'm looking forward to reading that, but I'm going to take a liberty here and speak on what we do...
For the beginner, in essence, we make boredom, or more precisely the reconciliation of boredom part of the training. As such, we have things set so that one learns to become very suspicious of a training that survives in terms of commitment only because it is in line with one's immediate or superficial desires (e.g. it's interesting, it's entertaining, it's fun, there's always something new to learn, etc.). We make it clear that Aikido involves a spiritual transformation of the person, and, as such, Aikido training therefore will require a reconciliation regarding a person's attachment to his/her desires - the one's that work to keep the objective/subjective world egocentrically oriented. For me, this is a much more fruitful approach when it comes to re-orienting training away from the more commercially viable model of scenario-based training than the usual (so-called "traditional") one of not concerning oneself with the beginner's interest levels.
For the more experienced practitioner, we use live training environments - as only principles survive there. We combine this with a very strong support system. How and why does this work? Well, the more experienced practitioner feels he/she already understands all there is to understand regarding the art, or, more accurately put, they are not at all ready to invalidate their understanding of the art as superficial (i.e. non-principle based). However, when you enter a live training environment, if your training is not principle-based, you gain a strong sense, regardless of how skilled one might be at self-delusion, that you don't know anything. One gains this sense because one feels that nothing one tried in the training environment worked. Of course this is not true, one does know something and many things of what they tried even worked, but that is the feeling. This feeling is necessary however for self-reflection to take place. Self-reflection is necessary for re-orienting one's training to take place. Of course, self-reflection takes place when an instructor shows one a cool little detail that is being left out, or when one does a simple drill that the person already feels they should be able to do but can't, etc., but this kind of stuff still makes one stay in line with "technique" training. So, there is no real re-orientation of their training, there is only a further refinement of it as it already is.
Now, when you use a practice like the introduction of live training environments, and you use that to re-orient their training, because you are looking to penetrate through the surface of the individual so that you can penetrate through the surface of the art, they will require a lot of mentoring (as understood by the ancient traditional/spiritual traditions).