Where does polanco play, and what happens to Julien in your scenario? Because it's very unlikely polanco his better than Julien has.
I'd listen to offers. If you can get a guy in AA that is a 45+or better, I likely make the trade. This is driven by my belief that they have three starters as good as him, for the playoffs, and that this FO refuses to take a chance on fixing the hitting issues, meaning I think they have little to no chance in the playoffs.
All that said, if they keep him, it's not an awful decision......