I have a Mackenzie too and agree about the paint job. Skin tones affect them too, my India Barbie is a Theresa but she's almost as dark as the light AA Barbie but with more of an orange tone.
As for the price change at thrift stores my mom used to work at a Goodwill and they'd use certain colors and codes to denote when something came in. Looking at the condition of her tag I'd say Kira is the new comer and they don't keep consistent prices on "Barbies".