I hope this hasn't already been touched upon, as I didn't read all 16 pages of this thread. But I believe the posture of the spine is more dictated by the respective positions of the pelvis and scapulae at address. If the pelvis is in a neutral position at address (and NOT in anterior or posterior pelvic tilt) and my scapulae are also in a neutral position (and NOT in a retracted or protracted position), the position/posture of the spine will be fine and in the best possible position to move as the golf swing dictates.
Anyone else use the positions of their pelvis and scapulae to dictate their spine posture/position?