Here is something worth noting.
The fastest American miler ever (Steve Scott) didn't find it necessary to do speed training almost every day of the week.
The fastest miler on the planet (Hicham El Gherouj) doesn't find it necessary to do speed training almost every day of the week. Anyway, not if you go by his competitive season training examples that can be found on the internet. He alternated speed/pace days with overdistance days.
Therefore, it seems as if it isn't necessary to do speed training almost every day of the week as Coe and Ovett used to do when they got close to or were in their racing season.
I believe that lots of speed training has its benefits but makes it so that you have to reduce your overall volume and therefore you can't continue to do frequent 10-15 mile runs as Steve Scott did. Or in other words, you trade speed/anaerobic fitness for some of your aerobic fitness.
Going by the limited amount of information I have, I believe that 3:43 miler and Olympic champion Noah Ngeny doesn't find it necessary to do speed training almost everyday.
Does anybody know about Steve Cram and Bernard Lagat? Which approach do they take (or took, in Cram's case)?