Once again, the answer depends on the typology of the athlete, not on the event.
Nixon was a type of athlete, such as Paul Ereng, Alberto Juantorena, Marcello Fiasconaro, Luciano Susanj, Tom Courtney, Bill Crothers (the best competitor of Peter Snell), Billy Konchellah and many other, having the attitude of a 400m runner, with a high percentage of fast fibers. Of course, for this type of athletes, THE MOST IMPORTANT THING IS TO ENHANCE THEIR LACTIC ABILITY, and only in a second time, maintaining the ability in producing lactate, they can try to enhance their LT.
So, OPPOSITE TO WHAT LYDIARD SAID, ANAEROBIC FIRST (Because is their main quality), and AEROBIC SECOND.
But, if we speak about other runners RESISTANT TYPE (like all the athletes running fast 1500m : Seb Coe, Cram, Ovett, Asbel Kiprop, Andre Bucher and many others), ENHANCING THEIR LT IS THE FIRST GOAL THEY HAVE TO HAVE.
Finally, there is a third type of athletes (the real SPECIALIST) that must work at the same time for increasing their LT and for increasing the Anaerobic ability. Athletes as Rudisha, Wilfred Bungei, Borzakovskiy, Mulaudzi, Johnny Gray, Barbosa, Doubell and many other belong to that category.
About Peter Snell, I think he was a RESISTANT type, so for him to enhance his LT was the primarly goal. But I cant accept the idea that what worked for Peter is the best option for everybody. And I'm sure that Lydiard, with his personal ability in understanding the real necessities in training of his athletes, if could be a coach in the athletics of today, could change a lot his plan, speaking about AEROBIC MOST IMPORTANT QUALITY FOR SUPPORTING THE LACTIC ABILITY THAT IS THE MOST IMPORTANT QUALITY FOR RUNNING FAST 800 and 1500m.