If we are truly thinking about contending for the playoffs, then I like him for our team as the 4th guard. In this situation we will assume Babb, Bogans, and Johnson are moved /cut and we need to pretend that Pressey, Wallace, and Young really aren't going to play - he provides a real scoring punch off the bench and also has range. Bayless got a lot of minutes on last year's team, there's no reason Thornton can't find some time this year. I am also not taking into account potential injuries.
However, if we can get anything of value for him, then of course we should move him. While he has a fit here, there are other teams who could definitely use him more.