You make some good points, I just think getting rid of Millar would be hard. He's under contract for one more year, probably one of the most popular players among his teammates, and does not have very much value across the league. Remember, he almost played in Japan.
Best case scenario to me would be keeping Millar as a pinch hitter (where a guy like him usually excels) and maybe for late inning power. Mienkewicz is a great player and I would love to see him every day.