Andre Johnson has potential to be the best WR this year. It would take a lot to pull him from this guy. You are very deep in the QB position and Aaron Rogers is definitely a favorite of mine. Schaub is a fine back-up if he can stay healthy, so I think trying to dish off McNabb is really smart. However, this guy already has Tony Romo, so I'm not sure he would bail on such an elite WR to have extreme QB depth. Further more, in a year where there isn't extensive WR depth, I would be shocked if he went with your trade.
I would try finding a guy with a weaker QB and offering him McNabb for some increased power in either your WR or RB options. I'm not fired up about SJax or Westbrook. Both can be great, but get hurt often and usually disappoint. @ WR - Greg Jennings will be solid, but it wouldn't hurt to beef up that WR section some. Try getting a Dwayne Bowe, Marques Colston, Roddy White, Wes Welker level receiver. That would really help you I think.
And for kicks - what do you think of my squad? viewtopic.php?f=44&t=444656