mileage takes years to fully pay off. yes, you can see benefits after 4 months no doubt, but 3-4 years of high mileage (100+) will result in times you probably once considered quite unreachable. youve just gotta gut out being tired sometimes, or even a lot of the times and look longterm. im still waiting for the results completely, but i have improved each season quite drastically:
HS-9:40 3200--50 mpw
frosh college-8:46 3000 (9:22 3200) -- 70 mpw
soph-8:23--80 mpw
this is all winter mileage...the summer before my soph year i avgd 85 mpw for 15 weeks and sucked in cross, but i came back and PR'd by 23 secs in the 3K and 35 secs in the 5K.
this summer i hit 90 mpw for 12 weeks, with a total mileage of 250 greater than last fall, and once again, not a great cross season, BUT, i am hoping for similar improvement come track season, which could put me 8:10 range.
conclusion: do all the mileage your body can handle and look LONG TERM, not season by season. by the time you graduate, you will be a much faster and stronger runner by looking long term.