Ahh....this is fun...
First, the Patriots (Maroney), Saints (Bush) and Colts (Addai) all recently invested #1 picks on RBs with good RBs on their roster.
2nd - Look at picks 10-20 and tell me who would you rather have? I'm guessing you'll say A. Davis. But if your evaluation tell you he's the OT version of Maybin, do you go with Davis because he's the right position or Spiller because he's the right talent? I have no problem with BPA if the player adds something that you don't already have.
Since Spiller is tied for the team lead in TDs and he has no idea what he's doing (schematically), I'll reach and say he adds something.