Picking up Anderson is just as big a gamble as dropping Levens. Anderson will continue to split time in Denver. I'd keep levens and hope for an injury to Staley.
You wont get anymore production outta Anderson than Levens. As a matter of fact, Anderson has not had more than 10 carries in any game yet, and he probably wont.
Levens may just give you 8-10 carries per game, but he will also get you 4-6 catches as well.