In a recent ESPN article, Chris Sprow mentions 5 Rb's that have a shot to become the next Sproles. One of the 5 is Speedy Stewart. I think Speedy if given an opportunity can become a serviceable player but he does not have the lateral or straight line speed that Sproles has and he has never been a factor in the return game.
http://insider.espn.go.com/nfl/draft2012/story/_/id/7624340/is-next-darren-sproles-2012-nfl-draft
http://insider.espn.go.com/nfl/draft2012/story/_/id/7624340/is-next-darren-sproles-2012-nfl-draft