Sometimes I think much of this phenomenon of improved flavor the day after has to do with the period of withdrawal of our senses from the smoke. As fire minders and pitmasters, we stand in smoke for hours tending fire and sampling food as it permeates into our clothes, hair, nose, and mouth. The next day after a shower (for married folk at least) and rest away from the smoke, with refreshed senses and a cleansed palate, we can more acutely taste the flavor profiles we have developed leading to greater appreciation and satisfaction of our BBQ.
A good analogy might be like an intense day after wine, whisky, coffee or cheese tasting. The palate slowly dulls for many until the senses can barely perceive the difference between zinfandel and cabernet, bourbon or rye, dark or light roasts, or goat or sheeps milk.
Just another one of my theories...