Compare a 1,4 to a f2? Well, the 1,4 let's in twice the light, do you want that and shallow dof as a result? The answer to that question gives the lens you want... add weatherseal too..
For me it makes sense, I use my lenses stopped down most of the time, but I can be in need of a large aperture sometimes. It's not to compare the amount of light the lens gathers, it's clear the 1.4 is twice as fast, it's to see how sharpness compares with smaller f-stops as well (again in my case). the 1.4 can be sharper with larger apertures but can be beaten by the f2 IS around f8-f11. I can accept some softness with large apertures, considering only a part of the picture is in focus anyway, but when I stop down I expect excellent sharpness all over, since it's likely that everything in the frame will be sharp then. Vignetting and mainly distortion are a big part of the equation too. Weather-sealing is a big plus but not a must for me, IS on the other hand can be an interesting feature....
I had the Nikkor 35mm 1.4 AI-S 20 years ago and finally exchanged it for 35mm f2 AI-S that was sharper, had less distortion an vignetting.
The 35mm 1.4L vs the 35mm f2 IS not like comparing apples and oranges, they are both 35mm USM, one is 1 stop brighter, one has IS, IMO it's worth hesitating a bit....
Not that I am comparing to him, but David Noton uses the 35mm 1.4, though likely on a tripod for landscape.
http://cpn.canon-europe.com/content/education/technical/david_noton_on_the_eos_5d_mark_iii.do?utm_source=newsletter-december-1-2012&utm_medium=email&utm_campaign=NewsletterMy guess is the old 35mm f2 was not enough IQ for him (picture 3 of the portfolio is a 35mm f1.4, stopped down to f8)