I know that continuous running week in and week out around 40-60 miles has a huge overall affect on running performance. The engine just gets bigger, the body takes on the specifications needed to perform the task, and when the specific workout regiment comes…you are ready for it. One thing which I miss out on is the mini race schedule I like to undertake for an event. You just get the racer's edge. You are battle ready. I tend to rely on past racing experience which has merit, but grinding out a few quick ones really helps you understand or sharpen your basic racing instincts. Your apt to make less mistakes.
I watch a fair amount of HS cross-country meets. The same people near the front don't always beat the same people week to week. As a runner you are always analyizing why this is. Sometimes you know (hard workout week) and sometimes you don't. Runs like Al's are similar. We all finish and think about what might have worked better. A mini race schedule helps in this regard.