I'm not a huge fan of stolen bases. Sure they are good, but when you get caught stealing, it is a real easy way to kill the inning. Getz is great at base stealing and it is an asset to the team. Alexei is decent, but he has gotten caught a little over 1/4 of the time he has stolen. That barely makes his steals worth it. The higher slugging of Nix and Hardy combined would mean more extra base hits. That combined with their defense makes me like that combo more.
I can see your argument about hanging on to Getz for his great base stealing and speed, but I think that Nix would be able to play great defense and solidify the infield next year (and i am a sucked for slugging and OPS).