Not suggesting it's wrong (keeping Smith @ Guard), but at the end of the day I would think you want your best 5 on the field.
As an example, if the Cowboys take a Center with pick 24, they may address OT but probably not until much later. You may be entering training camp with the likes of Asim Richards (or someone of similar ilk) being your best tackle if you're locking Smith in at Guard. For the record, I think Tyler can be exceptional at Guard but pending how this plays out, could sadly also be the most qualified to play LT.
At some point, I'd think you'd have to ask yourself what is more formidable. The Tackle, Guard, Center trio of Richards (whoever, pick your JAG), Smith, JPJ/Barton, or Smith, Bass, JPJ/Barton? At this point we can't guarantee the answer to that specific question, but I think pending an emergency, the Cowboys want Tyler playing Guard.