"World class runners have been doing various plyos/strength training, etc. since the beginning of professional running."
Yes, but it always seems to be looked down upon....
Baseball players used to never lift because they didn't want to "bulk up" and lose bat speed. Well common sense prevailed and now even HS players lift.
There still seems to be a disconnect between the few elite runners doing ancillary work and the HS and college runners still stuck doing NOTHING or the random old-school 1950s circuit style training on a nautilus type machine (3 sets of 15 reps, etc).
There's probably at least one thread a month that blows up into at all out war for and against strength training and plyos for distance runners.
As far as squats and loading the spine goes....if you're doing something like 3-4 sets of 10-15 reps, then yes that's going to be a problem. If you develop a strong core and limit the number of reps/sets then that's not much of a problem. Still, you could lessen the spinal load with other exercises such as front squats, split squats, DB lunges and squats, etc. You could even greatly reduce the load and do speed squats...which are probably more effective in the long run. But, I do believe you need to crawl before you walk, and walk before you can run. Basic general exercises first before the fancy stuff.
Alan