If I was stacked at RB (which you kind of are), I would agree with the poster above. However, just to play devil's advocate, RB depth is bad this year, and I don't know that you want to sacrifice your RB situation for an inconsistent WR1. I had FItzgerald last year, and I absolutely hated when Kolb was the starter. At least Skelton would throw it up to Fitz in triple coverage, Kolb is scared of letting the ball go. You have Jennings and Lloyd (who I think should be starting over Lance Moore) as your WRs, as well as plenty of bye week fill in WRs.
But Fitz can take any catch and take it all the way to the endzone, and he will singlehandedly win you some weeks. I would say Fitz obviously has the higher upside week to week, but his floor will be 1 catch, 4 yards, which is pretty damn bad. Sproles is always going to be more even keel.
I actually didn't answer your question here, but here are my thoughts on your situation, I hope it helps...
Help with mine? viewtopic.php?t=521163