Pick up Cadillac Williams for Week 15?

I have Warrick Dunn right now, but with the return of Williams, it seems like he won't get any goal-line touches. Williams' past two games back from injury, he has 2 td's. So I dont think dunn will get ANY td's unless he breaks some huge run for a td. This week they play Atlanta, who rank 22nd against the run. Should I get Williams and play him in place of Dunn? Good idea or bad idea?