"Do I care if the bolt and carrier are chromed lined, etc.? "
IIRC, they are all chrome lined, where the gas rings go, or at least they should be, but as far as a totally chromed bolt & carrier gos, no it doesn't really matter, MAYBE it would be more corrosion resistant, but the military doesn't use 'em, so you don't need 'em. I just bought a M4 upper and the dealer gave me the option of a chromed B/BC at no extra cost, so I took it 'cause I know they cost more, incase I resell it I could get more money.