Roffa,
Thank you for a clear picture of what data elements are useful and why. It corresponds well to what I had expected (other than the IAS for approaches, which I had forgotten about).
I was slightly surprised you didn't mention the vertical view of the stack, which I am lead to believe requires mode-S to be robust.
Equally, your list does confirm the predominate advantages for mode-s relate to the enhanced version which is not what GA is able or been required to fit. As such, my mode-s spend benefits no one. As Chevvron said, if all of the data that is now being collected at GA's expense where being shared out at marginal cost to people/agencies to make use of it, I suspect there would be a much more positive view of the deal.
M