I like both fartleks (simulate races better) and progressions (easier on the body I think) more then just 5 miles at X pace. Tempo runs have their place but decent mileage+good speed/power+a few race pace sessions should produce good results at 800/1500/3000 without many tempos. 4-5 miles hard once a week is enough for them. For 5k/10k/marathoners tempos are very important and should be done at least a few times a week when you feel up to it. 1/2marathoners/marathoners in particular run "close to the edge" during their races and should develop a good feeling of exactly where that edge is...for shorter track runners tempos are more of a support/strength thing instead of a direct practice of ~race pace. So whether they are overrated or underrated depends on the event and who you ask.
Oh and "Some Canadian", I completely agree...most people have way more potential at 200/400m then they give themselves credit for...speed development, like aerobic development, takes time. Both are crucial to a runners long term success. Unlike runningart I won't say that they are EQUAL in importance because clearly more time should be spent running, but sprint speed is often overlooked. There are a lot of distance runners fleeing towards the marathon, and even the ultra events now-say a runner in high school does sprints,drills,hills,weights and pylos and puts up a 53 400 and 1:55 800, but is not national champ. They move to the 1500 and run well but drop the pylos in favor of more miles, then move to the 5k in college and bag the drills, then move to the 10k and neglect the sprints and stop doing anything under mile pace, they try a 1/2 marathon after college and figure it's an endurance race and the hills don't help. Finally they try a marathon and consider long tempos at 1/2 marathon pace "speedwork". Slowly any speed they had is long gone and despite all the hard work and miles they struggle to run a 60 seconds quarter. They run well at the marathon but not to their potential, even though there is no way of knowing. They figure anything shorter surely couldn't help them run faster at the marathon, right as that is 99% aerobic...I know I will take some flak for this, but I don't really care all that much. Sorry if I got a bit off topic though.
here is a good article about it.
http://www.rxrunning.com/archive_runninglongerfaster.php