JD. I see your point, efficiency isn't everything but to me it is important.
I suppose to some extent it is going to depend on what you are looking for from your brewing, my main interest is in understanding the processes, having control of them and applying them to make exactly the beer I want. Much less about the brewing part, more about the recipe design and planning (not suggesting its right or wrong just personal motivations).
If I can get 10% better efficiency I will, not so much because every 10th brew comes with a free grain bill but because I enjoy the challenge.
The deciding factor for me is beer quality, if increasing the yield reduces the beer quality you have gone too far, same with every step in the process, adjust the water to suit the style, mash at the optimum temperatures and pH, don't over sparge, don't try to get too much out of the kettle (some should be left behind), pitch the right amount of yeast, manage the ferment properly...
Generally my brewhouse yield (efficiency to fermenter) is in the low to mid 80's%, From experience I know I can push that up to 90+% but at a price I'm not willing to pay.
Mark