The way the draft unfolded, trading down from 16 to take Lawrence would have been the best way to go. I think if the Cowboys knew that Jernigan would be available at 47 and Turner at 78, they would have taken the trade down in a heartbeat.
But that is exactly the problem, if it wasn't Jernigan, it could have been Nix, Hageman, Tuitt, Easley, Jones, Sutton, Reid, Ellis... If it wasn't Turner it could have been Jackson, Su'a, Bitonio, Yankey, Dozier... Or another position like they wanted D, but the value wasn't there so they took Zack.
The thing is, if they knew they HAD TO HAVE Lawrence you have 3 options:
a) Pick him at 16 reaching
b) Trade down to an area you feel his a good value even if the trade doesn't seem great value
c) Use other assets to move up to the area where you feel safe you can get him risking overpaying (most likely).
In general in such a team sport as football, it's very difficult for a player to be worth 2 players, some QB's and maybe a few elite guys at certain positions, even elite players are in need of a capable teammate or don't really make a difference.
Now in a draft that's supposed to be the deepest (best) in the last decade I would think what you want is as many picks as possible, especially if your team is considered extremly top heavy and thin.
But hey, maybe that's just me.