It's hard to say that the going rate for Alex Smith isn't a 2nd round pick, given that that seems to be the established price for a starting NFL QB from the Kolb/McNabb trades. People can go back and forth on whether they would pay that price, but I think people can understate how hurtful having an awful QB situation can be to the development and growth of a franchise. People have a hard time getting their head around an "above average" QB. They tend to just lump all QBs into two categories and haves and have nots, and either you got an elite QB who goes to Pro Bowls and appears in all the TV commercials or you got a "other" who are all equally about the same and can be equally swapped out. There is a point where you get such bad QB play that it singlehandedly holds back the progress of your entire franchise. You can't evaluate your WRs because the QB can't get the ball to them. You can't evaluate your running game because defenses stack the box on base down. You can't evaluate your pass protection because you find yourself in so many long down and distance situations the defense doesn't have to respect the run. You can't evaluate your defense because they all look like garbage by the 3rd quarter because they have to play 70-90 snaps a game because the offense can't sustain a drive.
Also, I think it should be mentioned that this isn't without significant risk for the 49ers. Putting all of your eggs into a scrambling QB who has never played a 16 game season, and his ability to stay upright, is pretty ballsy for a team with Superbowl aspirations. That team isn't as young as people think, particularly on defense. Alex Smith was carrying a perfectly reasonable cap number as an insurance policy.