Wagner continues to get the good players out in test cricket and has bowled some pretty good spells without a tremendous amount of luck, that being said, I think he's trying too hard at the moment for pace which is distorting his natural abilities. I wouldn't pick him but the other options are either Gillespie for another run at cricket, Bennett (although his fitness would concern me), Henry or Bracewell. That being said, I'd much rather Wagner over Bracewell and think Wagner is only a breakout performance away from becoming a very good consistent bowler for NZ.
The other thing to keep in mind is that at similar points in their career, Wagner has better statistics than Southee and comparable statistics to both O'Brien and Martin.
Ultimately, Sodhi still has a first class average of 49 - even with a 5/29 thrown in there. We should never select players who haven't performed a role at domestic level that we would consider "handy" in the test scene - i.e if Sodhi replicated his first class form and after 20 matches, had taken 45-50 test wickets at an average of 49, would we be happy with that? I don't see how we could be, therefore I don't see how he's been selected and why we're happy to select these types of players. Maybe if he'd come back this season and been dominating sides and lowered his average right down, but you can't even say he's done that outside of one performance
Compare that to the amount of domestic bowlers who year in, year out had great performances without getting a chance and it just seems like we're getting a little bit over eager on the basis of having a leg spinner for once.