Sickels had him rated 13th for 2013 at C+ rating. This kid may not be an elite prospect, but it seems like he should at least have a chance to make the big leagues. He seems to have a good power/speed combo, I don't know how any could reasonably expect more for Thornton or how this could be construed as a pure salary dump. He's the kind of prospect you need to fill up on and hope a couple pan out.
37 extra base hits in 343 PA this year, seems promising to me.