I like Darren Sproles, but he is not a top 5 running back. I would gladly welcome him in Dallas if there was a need, but there is not. The running back position is one of the bright spots of the Cowboys. I like Barber, Jones and Choice and feel all three can contribute to future Cowboys success.
Sproles is a very good change of pace back and an excellent return man. He is especially good as a kick returner.
Sproles has 544 yards rushing for his career. Most of that is due to the fact that he has played behind two very good running backs in LT and Michael Turner, so it limits his opportunities. Still that is nothing for a 4 year career. Barber began his career as a back up and put up 538 yards his rookie season.
Sproles is good and had a very good playoff run, but there are plenty of backs that can do what he did in the playoffs out of the back field. Some may have even put up better numbers. Now there are not a whole lot that could do what Sproles did as a return man. Of course they may be too valuable to risk losing to injury returning punts and kicks.