Depends what you mean by much sharper. The 50/1.2 and 50/1.4 are pretty much identical if most of your shooting is in the F2.8 - F16 range, the differences start to show up when shooting wide-open or close to it. At 1.4, center sharpness is about equal between the 50/1.2 and 50/1.4 with the 50/1.4 showing better corner sharpness. Things start to equalize by F2.0 with the OOF image still smoother when using the 50/1.2. Generally, I like the bokeh of the 50/1.2 better than the 50/1.4. Of course, If you need to shoot at F1.2, you only have one choice.
To me the 50/1.2's main claim to fame is what some folks call its biggest drawback. The fuzzy edge quality, when shooting at apertures in the F1.2 to F2.0 range, coupled with the sharp center image, gives a very unique look to a picture (almost like shooting in a tunnel). Not to push my gallery images, but all of the 50/1.2 shots were taken with the lens at about F1.4 - F1.6. I just like the way they look.
Jim Bielecki