Stuart, it really seems to be a nice lens, the 1.2L. I like the "review" too. And the picture of the rose... it is indeed much different at f/1.2 than at f/2.5...
If i may, i'd correct something: you say, " aspherical elements that deflected flare and only allowed on-axis light" - that is not completely correct. Especially for a 50mm lens, the angle of view is large enough to include on the image lots of off-axis light.
The main advantage of aspherical elements is that one aspherical glass/air surface can replace two spherical ones(with even better correction for the spherical aberration), thus reduces the number of lens elements needed. By this you get less flare (less air/glass surfaces), less weight (probably that's why the 50mm L version is much lighter than the SSC which, i guess, did NOT use aspherics). And by reducing the number of elements, reduces the physical length of the lens AND therefore, the need for a Biiiig front element too.
Aspherical glass surfaces were, however, pretty tough to make; mostly they were grinding them with a trial-and-error method, so they were expensive and complicated. Also the calculus of ray trace becomes more difficult with them. Nowadays, computer age, it's not really a problem anymore, see all the el cheapo zooms using aspherics...