My theory on a middle infielder is they need to be able to hit for avg, and just as importantly draw walks and not strike out too much. The key is having a guy with a great obp in the top of the order. You don't want your premier home-run hitter their or premier hitter(usually) because you want your rbi guys waiting to knock in your top of the order guys.
They don't have to be great stealing threats, but it is nice, because then you can have a single, steal 2nd, and have a runner in scoring position for the middle of your lineup.
To me Jimenez is just about the perfect leadoff hitter if he can continue to grow. Of course, I'd take Ichiro if we could get him.