Isn't it more likely that true spontaneity (when realized) is a fundamental understanding of oneself that transcends all aspects of one's life - and that proper execution of Aikido techniques is just one manifestation of it? That in this case, jiyu waza and randori would not be seen as developing spontaneity, but rather as reliable validators. That from a practical standpoint, do we really need to focus on and practice everything 10,000 times in order to perform it spontaneously? (Our lives aren't that long.)
And if so, shouldn't we be trying to find the source this universal spontaneity in everything we do, using jiyu waza and randori to simply test our current understanding?
Spontaneity of technique is manifest when one is in the moment, looking neither forward or backward. Aikido training fosters unification of mind and body in the moment. Technique emerges naturally as a function of the interaction between uke and nage and is not imposed by one upon the other.