I see nothing wrong with getting out front on a guy like Dez, or if a club is willing to extend their #1 knowing that he is an integral part of their future. If he is that good, go for it.
Moving early on a second WR, on the other hand, tends to be a problem. In fact, unless it's a lineman, I wouldn't go too quickly on the second guy in any position unit. That is, unless you already signed your alpha only to have something better fall into your lap. That's when you may have to deal from a position of strength and move the first guy along.
Jumping the gun on most guys is a bad idea, unless he's undoubtedly an alpha performer. And doing so after one good year... well, we have seen that plenty.