I feel more energized when I dive Nitrox as well. Sounds like a good randomized study. Blind a diver to the air mixture, set computer to air, limit MOD and repeat experiment a bunch of times with a questionnaire upon surfacing... but I suppose no one cares enough about the answer. If it makes you feel good, be it a placebo effect, why potentially ruin it with a science?
I did my own experiment:
nitrox dives + 3 post-dive magaritas = tired
air dives + no margaritas = tired
Which gas would you rather use?