With Alex Smith, we know what we get at this point: an average starter with a QB rating of 80 - 85 when mature and healthy: (385/641/4159/30/21 in '09 and '10)
Now, that's good enough to win some games with a good defense and running game, but it isn't enough to take you all the way...think Jake Delhomme in Carolina. This will be even more true in the future, with rule changes enhancing the role of the quarterback (QB rating has been going up over the last few years).
So, let's re-sign Alex for 2 -3 years and draft a rookie in the first or second round ...my preference at this point would be to draft a QB in the second (or third) round like Stanzi or Ponder. But if we have a shot at Locker or Cam Newton in the middle of the 1st, that works for me too.
If the rookie pans out and is a 90+ QB rating guy, then great. But if he's a bust, we still have Alex Smith to give you decent production.