Funny thing is not all leftovers will fall into this senerio. Some things are just horrible it you try it, like warming up a big mac or something. It definatly is common in your cassoroles dishes, multi ingredient things like mrs. G2's Paella, and most of the Pasta dishes. Couldn't think of the right words Bionic, but you got it the flavors "permeate" into the other things. Funny that other things baked, like a pie,cake or cookies do not change in flavor, they just stay the same from the oven.
I guess the factor involved is time. Makes me wonder how the flavor really travels, and what chemical changes occur to the rice or pasta, or even the meats? Obviously the juices are how the flavor flows, but in the case of the paella, would think the juices would make the rice glucky overnight, but they don't.
I know chemically, I can't figure it out, but I know its going to taste better next night.
My wifes Father was the kind of person who would never ever eat leftovers. I think he changed a bit when he got older, but when he was younger, no way would be eat them. He expected something brand new every dinner. He doesn't know what he was missing. The thought of a doggy bag was just undignified for him. Not me thats for sure!