Two things:
Fitting all of them into the lineup is more a function of the position they play than their left-handedness. Yoshida's field position, if/when he plays, is LF. That gives us 5 guys to play 4 positions, assuming you don't want Ceddanne at 2B. If Duran could go back to 2nd, I don't think we'd have a problem.
Last year, we were 24-21 against lefties. Our overall L/R splits were .746/.743, and our splits against lefty starters were a favorable .732/.779. That has to do with the structure of the team, but that's an amazing difference.
S, if you ask me if I want a lefty or righty, I'm choosing righty. But if I have a choice between a good lefty, or a mediocre righty, I'm picking the lefty.