What does changing colors a lot have to do with using crappy paint? You can get better paint for cheaper at a real paint store...
The thing about Behr is, they add a bunch of crap to it to thicken it up, so people can think it covers better. If you change colors a lot, you dont want thicker paint, cuz it will build up too much over time.
I don't know if paint quality has anything to do with the mixability or staying mixed or whatever. Not exactly my area of expertise; however scientifically, logically, it would start to sediment immediately - if it didn't then the particles (dye, flecks, etc.) would be "lighter" (less dense) than the paint base, so it wouldn't necessarily need mixing at all as it wouldn't separate out on you.
[I mean if a paint company, presumably a good quality one, were looking for ultimate customer friendly usability then they'd have an equalized system with dye/fleck that was the same density as their base medium to do just that. Just my opinion.]
That said; is extra thickness of paint on the wall a bad thing for some reason? I guess I would think the "adhesion" quality of one paint to another would be the more important bit, am I wrong? Like the whole reason I got Bher was because someone said it sticks well to itself and gives better coverage... Maybe I'm completely backwards, or I'm being overly logical/scientific about it LOL
(Though there is something to be said for availability up here, I think we might have a SW about 40 miles away, but there are no local paint places in the state that I know of, just big box stores [Lowes & Home Depot] that ship bulk from the lower 48. "Specialty paint" has to be shipped, which is flown, and the post office doesn't like mailing paint one bit. Maybe could barge it up, but that extra 500 buck freight fee probs ain't worth it for a single room heh)