A lot of mythology. Ctein was hoping to buy an Apo El Nikkor for one of his last big DT printing commissions. It wouldn't have made a whit of difference in his case, because the dyes themselves migrate a bit before they dry. That particular medium is simply not capable of extremely sharp images. Chris Burkett did drop a staggering sum of money on a 360 Apo El Nikkor for sake of big Cibachrome enlargements from 8x10 film. Ciba is a medium capable of holding extreme detail. But for 1/20th the price he could have purchased a clean used regular Apo Nikkor process lens and the prints would have been indistinguishable. I personally avoided the top-end Apo El because the MTF is so ridiculously high that one risks revealing every little scratch on the film base or carrier glass itself, or perhaps even the AN ring pattern. And I can't drop $12,000 or whatever for an enlarging lens, even if another one of those happens to turn up for sale in my lifetime. Very few were ever made in long focal lengths, whereas Apo Nikkors are abundant, left over from the printing industry. I have a set of them clear up to 760mm, mostly cannibalized for free from a giant retired process camera.
But when it comes to comparing between the ordinary El Nikkor and the process Apo Nikkor 360's, I have a good reason to own both, even though it would take a loupe to detect any difference way out in the extreme corners of a 30X40 inch print made from 8x10 film. One reason is that the regular El is f/5.6 is brighter wide open and hence easier to compose with when that overwhelming orange mask of CN film is involved. But in 360/5.6 fashion it's also a huge lens that won't even fit most enlargers. And sharpness-wise, it's best at f/11, two stops down, while the better corrected, far more compact f/9 Apo Nikkor is even sharper just a single stop down at f/11 - in other words, the same printing speed. And the Apos are precise over a far wider magnification range than the regular El's. That makes them versatile enough for 1:1 duplication work clear to huge mural work in the darkroom, or even view camera photography from macro clear to infinity.
There are subtle differences in contrast and microtonality which become even more evident in black and white printing. But is it a big deal for common enlarging applications? - No. It's a nuance, just like I said. And Apo Nikkors weren't even made in focal lengths shorter than 180, so are of little value in MF printing. But in that case, I do prefer Apo Rodagons (N's) because I am trying to squeeze the last drop of juice out the lemon. 6X7 and 6X9 film is pretty darn small if you expect it to compete in the same portfolio as prints made from 4X5 and 8X10 film, which is in fact a common situation for me. Yet if nothing existed except ordinary El Nikkors or regular modern Rodagons, I wouldn't complain. Sometimes I prefer the more ordinary enlarging lenses in color printing itself, because I want a tad less of an over-the-top look, or I might ideally need a particular focal length unavailable in anything truly apo.
So, if you happen to run into a bargain (or even free) apo enlarging lens in good condition, why not? Just realize that not everything labeled as "apo" is ideal for enlarging, and there are times it seems to be a marketing ruse. You need to do your homework first. I mentioned just the highly reputable Nikon and Rodenstock examples.
