@existential potential,
I have listened to his audios and videos (check u-tube) more than I have read, though I
have read most of "The Ending of Time" (K in discussion with the physicist David Bohm). His message is somewhat repetitive but it gradually reinforces the method of pointing listeners inwards on themselves and conducting self-enquiry. This amounts to non-prescriptive meditation in order to observe "the self" non-judgementally. I rate this activity to be as effective as any prescriptive system in promoting transcendental experiences ( experiences such as "dissipation of self" or "holistic consciousness", both of which might be called "spiritual" by some).
K's rejection of all organized religion (and nationalism) attracted many intelligent atheists with "spiritual leanings" to his door. His invitations to address the UN followed from this. His rejection of "guruhood" was also attractive, but ironically it was perhaps in keeping with a "less than saintly" private life.
I would rate K highly for those seeking something beyond materialism and who are suspicious of "cultish" systems.