The reason an 800m runner spends so much time doing endurance work is that the 800 has a much different energy demand than the sprints do. Ex: when you run the 400 (sub 50.0), you really don’t get into much aerobic respiration. But since the 800 is so much longer, there is a much more aerobic demand. A body cannot function that long without oxygen. So, like mike said, depending on the type of training you do for the 800, it could definitely adversely affect your speed in the short sprints. And if I know most college coaches, you’ll be doing quite a bit if base endurance work if he/she wants you to run the 800 at that level.