Good analysis emcampbe. I have the same general view.
I have a very high CPU rate, but it is because I am not fighting with a lot of high elites at very busy times between hubs. I have a lot of flexibility regarding when I fly. I realize I am fortunate about that, compared to many.
And I have snagged CPUs on lower economy fares.
Posters such as poor Kacee have to fight against many other elites on the routes flown, so he has very poor experience in snagging CPUs. (Maybe there also is a bug in his account that automatically blocks him from getting CPUs, or MP is mad at him for some reason )

So the fare paid only comes into account when competing with other elites in one's own Premier level.
Being a GS, or 1K, for the most part, is better for CPUs, but it still depends on routes flown, when, and how many other elites from one's departure airport are also flying on the route, and how many PAX purchase their seats that reduces supply for CPUs. Of course, size of the cabin is also a factor.
CPUs for me in 2015 tended to clear at either 3 or 2 days out. A very few cleared at 96 hrs. Also had several that cleared on day of travel.
Good luck to all with their flying this year. Pay what you can afford for tickets. Perhaps you will get lucky and snag some CPUs. If you want to sit up front for sure, then pay for it.