The way I see it, even though overall glass quality does seem to be improving, the differences between price class has not been removed. The ZEN ED and others have pushed the envelope quite a bit, granted. So for, me the point where ergonomics is the total deciding factor will come at whatever point the overall image quality meets what I need. In my case, it has always been, and will remain the overall package of the glass that will sell it, or not, to me.
There are a couple of cases where I would select on ergonomics is in the Alpha class. For me the Nikon EDG is too short and fat feeling, while the Steiner Peregrine XP feels wonderful to me. However, if I had an EDG, I could get along just fine with it. In this case the image of either meets my needs. Another case where ergonomics will kick a glass out of my consideration is that god awful center rod in the Monarch X. Prevents me from getting what I feel is the right grip. Other than these, ergonomics are usually kind of neutral for me.