Aoki ranks negatively as a CF but he ranks positively as a RF. He also, interestingly, ranks negatively as a LF but it's over a minuscule sample size. It's fair to assume he would be a significant defensive upgrade over Melky and he's a solid OBP guy who could fill Cabrera's role as a lineup table setter. He's just an average player really but he's an average player who fits pretty snuggly in an area of need. There should be other similar players (Saunders, Denorfia) available this off season so overpaying for him would be ill-advised unless the market completely dries out in which case overpaying for the marginal wins he represents might still make sense.