It will definitely knock him down a position or two in the first round, but that's it.
Wonderlic varies in importance by position. QBs and offensive linemen need brains. Though a few examples refute its importance--Dan Marino's 15 is prominent, though I have to wonder if he bombed it by a bad attitude--it really should be factored in.
But who cares about the brains of a RB? A CB? I wouldn't be worried.
But back in 2004 I caught some flack pointing out that QB Michael Bishop, who was exciting a lot of pats fans with his ability to throw 80 yard bombs, was simply not able to make the reads quickly enough in his head. His Wonderlic, a back-door IQ test, was pitiful.