If you're into lens collection, the 24-70 II will be boring 
I say that because now, I only have 2 lenses, and both are zooms, covers me from 24-200 (ok, 70-200 is only f4) but still. Used to lust over the 35L but since owning the 24-70, not much anymore. I still may buy one in the distant future but planning on just renting the fast prime I need, when I need it.
Gotta be honest, at one point I was thinking of returning it so I can get a cheaper zoom so I can fund my other hobby (cycling) but every time I look at the images it produces, can't make myself to do it.
So, like everyone says, if you're at f2.8 almost all the time anyways, the convenience of having to change FL with just the turn of a ring is worth the entrance fee.