It seems, ssg, that no amount of argument can sway you from the conviction that the only significant reason for using Flex / Reduced thrust is cost savings.
The truth is that significant cost savings do occur, but, (and it's a big but), even if no cost savings arose, I would (and do) strongly advocate it's continued use for safety reasons.
The probability of engine failure is directly proportional to the stress placed on the engine, and the widespread use of Flex / Reduced thrust very significantly reduces engine stress, and thus very significantly reduces the probability of engine failure. One of the predicaments faced by the statisticians in assessing the reduction in the number of engine failures is that as the said engines did not fail, no absolute figure can be placed on the engine failures prevented by the use of Flex / Reduced thrust. The one good comparison that CAN be made is with operators who previously used full thrust for all takeoffs, and then changed policy to using reduced thrust. The failure rate decreased dramatically.
So, even if no cost savings arose, or even if it was slightly more expensive, the increase in safety due to decreased engine failure rate makes such policy worthwhile.
Regards,
Old Smokey