From the research I have done on top 1500 guys, I have determined that most did at least 60 miles at some point, up to over 100. It appears that during the base, most likely winter, most put in decent miles, then as the summer rolled around they ran more like 50-60, then maybe even less to really peak.
The 1500 requires much aerobic power, combined with sharpened pH buffering and pure speed. The aerobic power seams to be maintained pretty easily during the peaking phase (40-50 mpw), but it is difficult to develop, which is where the miles put in over the years or in the base come into play. Not many have gone sub 3:30, but the first one to do was Sais Aouita I believe and he was known as a low mileage kinda guy. On the other hand, fellow Moroccan El G ran around 80 mpw and did everything fast, then I assume dropped some miles for peaking.
In conclusion, I believe that most sub 3:30 guys run around 80 mpw during the base, and then drop as big races come. Information can be hard to come by though as most great runners hide their training as they believe it was something unique to only them, and they don't want their secret out.