I did recently buy a ticket (LGA-DEN-SJC) <24h before I flew it. At the time, I figured I was not going to clear as F was looking pretty full. At the airport, I was #4 on the list as 1K (on I think a T fare), but I wound up being upgraded on the plane by the GA. It did make me think about the windows, but whether seats get held back is really a failing of revenue management, not the upgrade system itself. As a 1P, you're awfully low on the upgrade list (from speaking from experience last year).
Do you have
any idea that you will need to be in a particular place at a particular time (and instead, these plans just occasionally change/fall through)? If so, since your company is willing to drop the money for full Y, could you book earlier (in full Y) and refund if plans change?
How do you know that F is being filled with upgraders in advance? The other threads in this forum seem to suggest that no one is getting upgraded at the 72 hour window, so which is it?
I've stopped relying on CPUs and mostly burn RPUs for the flights that count (redeyes). Anything else is a pleasant surprise at this point.