Thanks for the input on mine!
I actually would rank Marshall higher than Dez, but then again, I live in Chicago
I agree with the others that you might SLIGHTLY upgrade your team, but that you could be helping someone else out way too much. I know it's not always good to think about what the other team gets from trades, and as long as you're improving your team that's what's important, but Murray COULD have a top-15 year this year, and Marshall receives 75% of the Bears' targets.
Even if Marshall is 30, he'll be a beast in CHI for the next 2-3 years minimum. You could say Dez has more potential for longer success, but he could also have a mediocre year if Miles Austin stays healthy, if Jason Witten repeats his resurgent year from last year OR if Romo gets injured. All things considered, I just think Marshall is a lock for top-10 points, with odds being he's in the top-5 in any league format, while Dez could finish just outside the Top-15 if he doesn't connect on enough long balls.
Juice isn't worth the squeeze IMO. See if you can get a better deal if he wants a 2-for-1 with one of ur WR/RBs. After all, you're in the driver's seat not needing to give anyone up, and he looks like he needs quantity of keepers over quality.