The Rockies would like to improve upon Melvin Mora, which is understandable, given Mora's age and bat. But that doesn't mean bringing Kazuo Matsui back is the answer for the Rockies, who are interested in the infielder.
Matsui was fantastic during his first stint with Colorado, hitting .300/.353/.426 on his way to a $16.5MM deal with Houston. But two and a half years later, the Astros are about to release him because he's a different player. Matsui remains an efficient base stealer and UZR suggests his recent defense has been average, but his .141/.197/.155 line would not represent an upgrade from the Rockies' current option.
At 38, Mora is not likely to rediscover 25-homer power, but his .250/.308/.350 line is tolerable for a utility player. Mora's value comes from his defense; UZR rates him as an average defender, and he is versatile enough to play around the infield.
Replacing Mora with Matsui would leave the Rockies without much defensive flexibility. Matsui hasn't played a position other than second base in the major leagues since 2006 and he has never played either corner infield position at the highest level. The Rockies, who have used Mora at first, second and third already this year, rely on his versatility, since their bench includes pinch hitter Jason Giambi.
If the Rockies could carry a 26th man, then adding Matsui in the the hopes that he can recapture his batting stroke wouldn't hurt. But in reality, adding Matsui means removing someone else from the team. They aren't about to go to a six-man bullpen, so Mora or Giambi would have to go. Giambi hasn't hit like he did last year, but the Rockies seem to like his clubhouse presence and power bat.
Matsui does not seem to fit in Colorado, but let's not overstate the Rockies' interest. Just because they have some interest in bringing him back doesn't mean that they're actually going to sign Matsui and give up on either Giambi or Mora.