We have enough speed to win. Pure speed is overrated; talent and guile are more important. Who cares how fast Bledsoe runs when all that matters is how quickly and how well he throws? What does speed matter in a WR if he can't separate, get open or the QB can't reach him when he is open? Who cares how fast a RB is if he crashes into the backs of his linemen or can't elude or break tackles?
We have Thompson, Julius, Glenn, Copper, and Price on offense for pure outside speed but these guys are complemented by Barber and Crayton who are shifty and find the in-between spots that are open in the defense. Key and Witten separate with power and guile.
On defense Glover, Ware, Burnett, Dat, and Newman are as fast as they come at their positions-- they are complemented by guys who are physical and know how to play.
Obviously, what I'd like to see Dallas gain:
1) A WR who is both powerful and fast. It's nice to see short passes turn into long gains (YAC).
2) A RB who runs with power-- possibly a crushing FB like Lorenzo Neal. We need a short yardage bruiser.
3) A ball-hawk FS.
4) A powerful OG who can move.
5) A first class OT.
Only the first position requires true speed.