If Booker weren't so balls-out awesome and frankly even sort of wasting his talent as second option, Welker would absolutely have earned a starting spot on this team by now. As I have said several times over the last day or so, Wes Welker pisses excellence. The guy who said that if we had 53 Welkers, we'd be a great team is absolutely right. If everybody played like Wes, this team would be unstoppable.
It is becoming clearer and clearer to me that Nick is setting himself up to move Booker in the offseason. I'll be sad to see him go, but my guess is that Welker will continue to play well and Hagan will emerge. I don't know which one of them will start next year, but I think that's your clear top 3 on the 2007 roster when you add in Chambers (based on what we can tell right now about 2007, which admittedly isn't jack squat).