The 35mm F/1.4L is a great lens, on a full frame body. The aspects that make it great decrease when you put it on a crop body. It's narrow DOF, its low light abilities coupled with a camera like the 5D II make it a very special lens. On a crop body it would still be a very good lens, but some of the potential you are paying for will not be utilized.

It is probably over due for an upgrade, I would be the first in line for a 35mm F/1.4L II. That wouldn't stop me from buying the current version.

I agree with Daniel, you will gain some resolution and contrast. It will come with a premium price.

For me it ranks at the top of my list for lenses I need for full frame, on a crop body it would be a focal length I am not often drawn to.