i have done a lot on a little training...but did find that i needed to regenerate at some point (go back to base training).
After experimenting with a day off in my last year of college, I slowly converted to running every other day - and doing all quality (essentially my off days which used to be easy milage days were replaced with 0 running and instead i stretched and did some light rowing).
at my best at around 40 mpw (4 runs per weeks) i was able to run 23:45 8K, 1:03:00 20k for my all-time bests...i think this worked however because i had been doing 14 milers the summer prior nice and slow once a week (so i had some base & endurance and simply started uping the tempo on these 4 runs) and had 5 years of college milage 70-100 per week 2 yrs prior. First year after college probabaly ave 60 at most (with some weeks less in winter) and 40 (during the second years when i hit these times)
Typical week-
Sun - longer day 10+ (but quick 5:30-5:40 pace)
Tues - hardest day - 8-10 (sub 5:30 - to as fast as 5:10 for some of it - usually a progressive steady state)
Thur - pre-meet workout - 6 miles (did the first 3 progressive 6:00, 5:40, 5:20) then 1 X 1 fast road mile (4:40 to as fast as 4:20) and wihtout stopping 2 more miles (around 6:00)
Sat- raced (any where from 2M-1/2M) and set PR's just about every weekend racing 3 times per month.
my training was pretty much centered around steady states...with no track workouts and no slow days (i actually think some track workouts would have been helpful) but the one workout i really should have done was the one long slower run (that Sun run should have been slower and longer every other week: 15+ at 6:00+)...but i never trained tired since i was coming off a day off in most cases and that really helped me workout faster (yet feel easier) anyway that's what worked for me. This didn't hold year-to-year however, most likely due to too no base phase (as i did not go back to it) so as each subsequent year passed i got further and futher away from those faster times.