This is probably not a popular opinion but hey - this is a message board and this is my opinion ! I would not draft a QB this year, I would roll the dice that Romo has at least 2-3 good years left (all dependent on his health - which I expect to be better with no off-season surgery). I would stay with Weeden as the primary backup and Vaughn as developmental QB. Romo sat for 4 years !
I think Weeden is an OK backup, and the longer he sits behind Romo the more comfortable he becomes. Not a long term solution but good enough to backup and come in during mop up, end of game scenario's. As he did in the game he threw a TD in mop up duties.
I agree with the premise that with Romo still playing strong, we cannot take a QB high, and have him sit 3-4 years - his rookie contract would be up by the time Romo retires and then we would again have to pay big money to a unproven QB. We would need at least a few years on their rookie contract - ala a Russell Wilson type Scenario.
Play Weeden as the backup, trust that it will get better as he practices every week and the off-season - as he should have been given when drafted. Continue to develop Vaughn, and he either surpasses Weeden by the next off season or we again address the position next year (Only probably 2 years for a QB to sit behind Romo, giving the team 3 years on that rookie contract.)
I highly doubt we will get lucky enough to have an undrafted QB play up to Romo's standards, so we will at some point have to draft one reasonably high - just not this year ...