There is one thing I noticed about Salazar, he is far more conservative in his training than others.
He is high mileage, but other runners have done more mileage. There is a speed component, but I have heard him discuss how he tends to use more of the Oregon method of speed work at date pace. So speedwork is a gradual buildup to the peak of the cycle. He also gives time off at the end of a cycle to recharge.
There isn't really a pushing of the envelope, with the exception of the post-race workouts.
Salazar uses gimmicks like an Alter-G treadmill, but the clear goal is to get aerobic development without the stress on the bones.
I think a lot of this is due to Salazar's reflection of his own career. He was cooked by the time he was 25. And he ran to push the envelope.
Mo Farah and Galen Rupp are still running better than ever and are considerably older than when Salazar was done. Salazar simply took the philosophy that it is better to have a long career with gradual improvements over the course of a decade plus as opposed to a short burst of brilliance.