Spontaneity can't be over thought.
We are really talking about something more than mere spontaneity. We're talking a little more on the spontaneous creation of technique, and spontaneous useful movement. Really, more than spontaneous that probably means reflexive patterns and muscle memory.
I'm now third dan, how do I move forward and develop better movement?
Now that I teach, how do I best help to create the circumstances for development of apparently spontaneous useful movement in a student? It is a focus of study by militaries and athletes, but I don't see that being applied to Aikido so much.
IMO, there is some benefit to planning out training, and discussing training methods. Repeating kata is necessary, but something needs to happen next.