The other concern is people are likely to have many EF-S (or other cropped) lens in their gear. It stops people (for amateur purpose) from moving into full frame.
In your example, people using crop bodies tend to pair with the Sigma 30mm f1.4 instead of the 35mm F1.4L. The result is just so close for output...
In my opinion, short to medium range zoom lens made by Canon is performing so bad (compared to the price tag). There are so many lemons for the L series. Surprisingly in my experience, the best zoom lens I can recommend in the Canon lineup is the 17-55mm F2.8IS. You won't even get a "level" upgrade even if you are using 5D2/16-35f2.8II or 24-70 f2.8 combo.
Last week I picked up a Zeiss ZE 21mm f2.8. It's the best wide angle lens (I would call it a beast) I've seen so far, result is just amazing and pleasing...