I don't see any need of #12 where it is not required I even have some problems with where it is required. I will say that I wire homes with more branch circuits per Sf than those of my competitors but I don't think running #12 would help. After all I have lived in a house all my life and I think I know what kind of load people are going to have in different rooms. Wiring bedroom receptacles with #12 is a waste of money and energy and time. If you need a space heater in your room you have issues with the HVAC guy.
We use 14 on most cicuits and 12 as req. As stated previously, it's all about layout and design, properly located panelboards and common sense. Any idiot can overbuild and make it work. Hey, why stop at 12? Wouldn't #8 (pigtailed to #12 @ the boxes - 5S deep) be even better? Get real Julie - your usually right on but not on this one. Engineering is supposed to make things work better for less installed cost.