If your defense is good enough, and your ground game is sturdy, a game manager who does not make mistakes is all you really need. This may be before some of your time, but Jay Barker was, in 1992, like Baus for the Crimson Tide. He specialized in handing off the rock and in not screwing up by making turn-overs. He was, at best, an average passer.
The point I'm making though, is that if your defense is not stout, or your running game able to take over a game against lesser opponents, then you need something better than a game manager at the helm. Because a game manager QB will not replace the loss of not having those other assets. It does not mean that you will not have a winning season, but that you will likely not be in contention for BCS type games. If you had the 07 defense and running game then, IMO, Joe would be adequate for the job. But if you feel that you do not have the defense and running game to compensate for quarterback play, then it would seem that the best option would be to try to find the guy who has the best chance at improving to more than a game manager, and go with him. To be fair, the down side is more (in that young guys turning over the ball can lose close games), but the up side is greater (if the young guy "clicks" you have a shot to advance to a better bowl or conference championship).
For a new coach trying to earn a long term contract, perhaps it is a wiser course not to throw the dice on the hope of developing a younger player. Having one or two wins less - but a more experienced quarterback ready for a 2012 breakout year - will seem like less of an accomplishment if those two extra losses means you are unemployed and watching it on TV.