I want to underline the importance of basic speed for a distance runner.
I think that too often the real top end speed work is neglected, which is very important to emphasize especially in the youth. If you neglect the speed year after year, your basic speed will deteriorate as you get older. The shorter the distance the sooner your basic speed will become the limiting factor.
In these days the top 5-10k runners are able to run 5-10k in pace of about 15,5-16 seconds per 100m. You can calculate a rough estimation of the 100m, 400m, 800m, 1500m and 3000m ability of these runners, based on ~2,5 sec difference per lap pace (instead of the 4 second rule which suits better for a middle distancers). So a typical 13.00 5k / 27.00 10k runner which comes more from the endurance side, could have the speed of about
100: 12,5 (50 400m pace)
400: 52,5
800: 1:50 (55 400m pace)
1500: 3:35,6 (57,5 400m pace)
3000: 7:30 (60 400m pace)
5000: 13:00 (62,4 400m pace
10 000: (64,8 400m pace)
Of course a 12,5secs 100m or 52,5 400m speed isn´t likely enough for 1:50/3:35 800/1500 so could use a 3 seconds difference or so when coming down in sprinting distances, but also have to remember that distance runners usually suck in starting from the blocks.
An example of Mo Farah based on his real and assumed pb´s:
100: 11,67-12,04 assuming 2,5-3 secs difference vs assumed 400m pace
400: 49,68-50,68 assuming 5-6 secs difference vs 1500 pace
800: 1:48,69 (54,34 400m pace) From 2003, isn´t in line with the 1500
1500: 3:28,81 (55,68 400m pace, +1,34sec)
3000: 7:32 (60,3 400m pace, +4,6sec) Could be faster based on 1500/5k
5000: 12:53 (61,8 400m pace, +1,5sec)
10 000: 26:46 (64,2 400m pace, +2,4 sec)
Farah could have been even faster at 3-10k in top shape
on pure time trial type-races which were more typical in the prime of Haile, Daniel Komen, Kenenisa Bekele (pretty fast still) etc.
So a good basic speed seems to be quite important also at longer distances. There has been runners like Bob Kennedy (a 3:38 1500m demands some speed though), Ingrid Kristiansen, Paula Radcliffe (400m pb 58.9, 800m 2:05, 1500m 4:05...) etc. whom was able to run closer to their top speed than most of their opponents. It´s impossible to know how fast someone was at his/her prime in the events from 100m and up, but most were quite fast at least before the longer distance success.
To sum it up, what I have seen in the Letsrun.com forum, often the first thing what I see in someone´s training plan/program is the total (or almost) lack of the basic speed work. There can be the strides almost every day, and/or "speed work" which is done at 800-mile paces, but the frequent speed work in the base phase done SHORT and FAST (from ~50 to 150/200m), with long recoveries is what seems to be neglected. How can especially so many middle distance coaches/runners seem to think that you can be at your best in the season, if the systematic basic speed/anaerobic capacity (anaerobic POWER in the pre-season) work hasn´t been included in the base phase? Sprints (and maybe some weight training) also helps to keep your bones and joints strong and your stride efficient. And do not forget all of the hard, systematic endurance work of course, to be able to use the speed you have... Just my thoughts.