I'm slow by LRC standards, but consistency in training took me from a ~20:00 5k to a 17:5X 5k. Nothing special, just going from running 20-30 mpw inconsistently to 40-60 mpw, every week, with some quality every week. I "only" took about 2 years to get to that point, progressively, and I have a strong feeling/hope that I will continue to get faster.
I also am a big proponent of longer, more moderate workouts. For example, instead of 400m repeats hard, I do a lot of 1000-1600m intervals at threshold pace with short rest, and a lot of tempos and moderate (slightly slower than MP) running.