Dallas has six talented WRs, apparently. Mingo and Brown are two outside guys with starting potential, while Lamb, Pickens, Flournoy, and Turpin fill each very specific roles. Do you need two depth guys?
I always felt the answer was yes, especially if either can play on ST's. I prefer six WR's, because you can run five-wide formations with all receivers in the face of injury, family emergency, sickness, or suspension. You still could with TE's or backs, but I also like being able to run deep shots on successive plays without worrying about who got tired-- just rotate in another guy.
If you expose one now, past results aside, you will lose him. With the coverage Dallas gets, there's nowhere to hide them.