I tend to agree with your assessment on the bulk of the pheasants. The Big Sioux drainage is where I do the vast majority of my pheasant hunting. It's alright, but as you said, I don't see a whole lot of variation from one year to the next where I hunt. The exception being the devastating winter of 96-97.
When numbers were at their third peak in the early 2000's, I remember going to Redfield on Sunday of the opener and the big thing was how fast your group could limit. And this type of thinking was pretty common in a lot of the traditional hot spots. This might be anecdotal, but it has always seemed the James River drainage and Missouri River drainage were a step above my stomping grounds. Again, it could just be the experience I had and nothing empirical.
All that to say, I really dig seeing big numbers of pheasants, but am happy to jump on a WPA and chase the handful of birds that are on that ground at a given point of time. Peaks, valleys, hot, cold, happy wife, angry wife, whatever. Sage and I will go do our thing and constantly be wishing for more.