When I think we replaced Kelly Johnson with either Maicer Izturis or Emilio Bonifacio I immediately think we have upgraded. After looking at the numbers I am not so sure.
The numbers most often quoted in this forum I believe are OPS, wOBA and wRC+. When we compare those stats from last year this is what we get.
Johnson .678OPS, .299wOBA 86 wRC+
Izturis .635OPS, .287wOBA 82 wRC+
Bonifacio.646OPS, .290wOBA 79 wRC+
Johnson .717 .315 & 92
Izturis .722 .318 & 102
Bonifacio.758 .335 & 109
Johnson .866 .378 & 129
Izturis .684 .307 & 92
Bonifacio.648 .292 & 75
Johnson turns 31 next year, Izturis 33 and Bonifacio 28. So we can't expect Johnson or Izturis to improve much, Bonifacio is the only one who is still in his prime hitting years.
Defensively, Izturis gets the edge as he has a positve defensive metric according to FG over his career. Johnson is very close to 0.0 and Bonifacio is in the negative.
What I see is, Izturis starts over Bonifacio and we have had almost a wash at starting 2B. Bonifacio comes in off the bench to spell guys and pinch run which will be a great improvement over Vizquel. But overall, it is very close to a wash.