Agreed. I doesn't make sense to DFA Chris just because he's making more money than he's worth. The money he's being paid is a sunk cost you're paying no matter what. The question is whether he's better than your alternatives.
While Chris is never coming close to 2013 again, he's hopefully better than we saw last year. As you said, he still hits lefties. Though that is an understatement. Chris destroys lefties. As bad as last year was he still hit .395 against them and seems to be doing about the same this year.
With as lefty heavy as this lineup can be sometimes, Chris is a nice piece to have. Overpaid but still worth keeping. If someone offered to pay his contract I'd deal him in a heartbeat but he's not someone you DFA.