Something to think about:
Denver led the NFL in rushing yards last year, in spite of defenses knowing that they could pretty much put 8 defenders in the box on almost every single play because they knew that Tebow's throwing wasn't much of a threat. IE, The Broncos led the NFL in rushing with everyone they played knowing full well that they were going run, run, and run some more. Now, insert Peyton Manning for Tim Tebow, and suddenly you have a deadly passing threat to keep defenses from focusing on the rush...ie, while they could get away with it against Tebow, if they try to stack the box against Manning, they are going to get destroyed, playing against average WRs or not. Manning will find the open WRs that Tebow couldn't, Manning just being there makes their WR corps better in the same way Tom Brady made stars out of Wes Welker, Deion Branch and Troy Brown.
I think we are making too big a deal out of the Broncos deficiencies on offense. A superstar QB like Manning can be a fix for a lot of problems.
I agree here. If there's anybody that can make nobodies into somebodies, it's Peyton Manning. Guys like Austin Collie, Pierre Garcon, and Dallas Clark were GOLD with Manning throwing to them. He's gone for one year and you barely hear from any of them.
Manning can turn Decker and Thomas into the best receivers in the league because like you said, Manning will find these guys. He has the uncanny ability to throw people open so the ball lands right where it has to be. If you thought this team was just "good" under Tebow. Imagine the damage they can do with somebody like Peyton Manning under center.