Langford just hasn't played enough to know one way or another at this point. I like cost controlled guys, so unless something really shakes out, you don't go out of your way to trade him when his value is at the lowest point possible.
On the other hand, we seem to know what we have with Waters, Edwards, and even Tacko to a point, so probably time for those three roster spots to open up next year for either vet min guys, and/or our first round pic + Yam if he comes over.