Still don't think that max aperture difference between 1.7 or 1.8 versus 1.4 alone is not worth the extra cash. Not even talking about a stop. Other qualities, focal length, quality of glass, blade count, etc.. will be the deciding factor.
For an intimate low light situation... I like 35mm. At that focal length f2 versus f1.8 (or even f1.4) isn't that big a deal... especially at wider angles which can be handheld at slightly slower shutter speeds than telephoto focal ranges.
This is pretty much the same for 50mm focal lengths. Its not a consideration of f1.4 versus f1.8 but the other things that the 50mm f1.4 brings to the table. Same with the new 85mm lenses.. many stick with the 85mm f1.8 over the f1.2L because its far more compact and the price difference is HUGE.
Now at Canon 135mm f2L is really a fast lens worth the extra cash. Why? Not because of the fast max aperture but because of the max aperture of f2 PLUS the long focal length and its wonderful contrasty glass. It's not a 1.2 or 1.4 but its the fastest telephoto in the Canon line.. and worth the extra cash because its fast AND long focal length AND contrast.
Simply pointing out that a blanket statement that faster is worth it is over simplifying everything.