I needed to make this response/comment a new post, as it was too long (and important) to be potentially lost in a mere comment:
Firstly, running less for improved performance is an interesting concept, and one that is not totally new. In college, under the great Coach Truce, Chris Cody and I had read an article about running called "less is more." I think it was actually referring to an older runner, perhaps over 70. We presented this concept to Truce as an argument that we were being asked to overtrain. It did not go over well, as I remember.
Anyway, here are my main points regarding the new paradigm:
Firstly, in principle, running less and faster may be a good idea at our age (50) and it may work. However, I have a few concerns and comments. In your previous post, you alluded to your reduction in performance as related to inclines or hills. So, the obvious solution is to eliminate hills or inclines from the workout, and see what the results are. Unfortunately, with your current changes in training, I think you will be unable to determine whether running hills or inclines was adversely affecting you. As a mathematician, you understand the concept of multiple variables, of course. If you review your new paradigm, you will note that you have changed not one, but as many as four variables in your new workout program: removal of inclines, reduction in per run mileage by approximately 50% (or more), running at a different speed (faster), and doing all your running on a track instead of partial road runs. If your interest is in determining whether hills was the ultimate culprit, you may need to go back to 4 miles per day, similar speed runs, and part road part track workouts. If, however, your interest is simply in trying some changes and seeing if you perform better, then your current program may work.
My second concern is that you have subltly and perhaps subconsciously begun to adjust your previous goal of a sub-6 mile by stating that you would try for sub 6, or perhaps just a 2:45 half instead. I would like to see you stick to your sub 6 goal. By eliminating that goal, you are admitting that you may not be running enough mileage, and although I am all for relatively low mileage with good quality, 1.5 to 2 miles per day is probably not enough to garner a sub-6 mile.
Well, those are my primary concerns.