Jimmy, thanks for the input. As you note, the cost is relative.
Saving fuel has been a marketing ploy for quite some time (dont forget the carbon you save!)
TOC is far more difficult to show benefit, for all the reasons you mention, with all of the real time variables, especially winds and bleeds.
Time of flight that must be considered to see potential value if cost is the issue vs time.
TOD has far more value, especially in a coded procedure. The original 'idle descent' sales pitch was crap, especially mixing RNP and non-RNP traffic in the terminal environment, with ATC managing the flow.
Quickly learned there was no value, and actually penalties.
TOD management to FL10, now that is much different. A simple waypoint on the STAR to the system to calc and one at FL10 will optimize TOD for the ac real time (we can add a time constraint), will provide the optimum fuel, time and flow management for the flight.
Driving as fast as you can, to sit in a hold pattern?