A good movie on the subject I just watched is What the Bleep Do We Know!?. If you have a hard time reading heavy stuff, this movie is at least entertaining and thought provoking. It made my wife and I think about a lot of things. Very relevant to aikido and self improvement. To me it is explains the essence of KI.
A very interesting movie, which I believe speaks indirectly about ki.
I see ki development to be a spiritual pursuit. Born and raised a Catholic I have since stepped out of organized religion and the church to pursue a personal path. I mean Jesus only went to church once and that was to trash the place. If there is one thing I learned from him it is that questioning and challenging conventional ideals and practices is essential to our spiritual growth.
Having seen the positive effects that meditation can have on society (recorded drops in violence etc) and the way our thoughts and words affect not only our internal makeup, but the makeup of water (and who knows what else) I sincerely believe "plus ki calls plus ki".