To answer the question......YES the Cowboys should be worried about the WR positon. In my opinion it is the weakest position on the roster. The secondary as a whole is solid with TNew, Henry, Glenn and Williams and the corners from last seasons roster in depth roles plus the rookie from Ball State at SS. FS is a concern but it is just one position out of the bunch and may be hidden by the surrounding talent. Same can be said about the offensive line and the RT position. The DL and LB core got added depth thru the draft, the TE spot got Campbell back to go with Witten and Robinson (both Pro Bowlers). The QB spot got Bledsoe to go with prospects Henson and Romo who have a year in the system under the belt. The RB spot has "21" (Julius Jones) and got added talent/depth thru free agency and the draft with A Train and Barber III respectively.
Wideout has two thirty somethings coming off of injuries, a 1st rounder who has yet to "breakout" and needs to learn how to position his hands for the 1st time in his four or five year career and a bunch of low round players or undrafted players we hope "breakout" much like we did with "Mr. Intangibles" Randall Williams. I believe that Key and Glenn can be effective this season especially since age shouldn't affect Key's game since it is not predicated on speed however, my concern is the fragility of Terry Glenn. Glenn if healthy is very dangerous but at this age the injuries to a player who is somewhat slight of build (relatively speaking since most of the guys we consider small in the NFL are ripped up and make us look bad) is more likely to occur than not. Next season this spot needs to be made a priority.