Kelly is a better defender at 2nd base than Infante, he's better on the bases and has more power. Overall Johnson isn't that much better, but if we can put him at 2nd on the cheap and move Infante to a super-sub role than it improves the team, it's really that simple for me.
2B is not an issue. Infante is not a bad 2B and there is no benefit to making him the super-sub instead of Santiago. The market this year is strange in the fact that I have not seen many deals "on the cheap." Quite the opposite actually. I think it more wise to make a move that is necessary. Moving Infante out of a starting role is not necessary.