Well...that changes things rather drastically. Here's how I see it now:
Johnson > Gore - I don't think this is really much of a big upgrade...I think Gore has something that CJ doesn't have and that is the ability to be "the guy" and take the 250-300+ carries in a season. I think Johnson comes across to me as the kind of back that will always need to be part of a 2 back system. Gore isn't exactly old either, he's just 26 to CJ's 23 which for a RB could end up meaning not much with how short some RBs are truly able to play at a high level. I do have Johnson higher on my keeper/dynasty rankings though, but that one's marginal at best I think.
Jennings >>>> Crabtree - While Crabtree has the potential to be as good as Jennings, I've never been one to like to deal proven for potential. Jennings has a better situation with a very good QB and he's proven he can be a productive receiver. Crabtree has all the tools but he's playing for a run first coach (Singletary) on a mediocre team with some huge question marks at the QB position. Jennings is a guy I have rated very highly for keeper and dynasty leagues and I wouldn't be too quick to get rid of him.
Gonzalez >> Burleson - The thing here though as well is if Burleson is ever able to stay healthy, he could be as viable a WR option fantasy wise as Gonzalez is. You have to give Gonzo the edge in situation playing with Peyton and opposite Wayne, but he's truly option #4+ there in that offense...Wayne, Clark, and now the RB duo of Addai/Brown will almost always all take priority there. He's stepping into Harrison's role but he's not Marvin Harrison. Burleson will be helped by the addition of Housh as TJ will draw all the coverage and if Burleson stays healthy he'll be a solid contributor I think.
So, all in all I'd pass on the deal. I think you slightly win in the Gore/CJ and Burleson/Gonzalez parts but you lose way more in the drop from a proven Jennings to an unproven Crabtree who could still be a couple seasons from really developing as a legit fantasy WR. I'd stand pat.
I honestly don't see anything on his team that will greatly be an upgrade over what you have...if you're going to look for a deal, I'd look at another team.