TBF, NZ have basically had Southee and Boult take all their wickets in this series. It does seem the stirring of Broad about the new ball has done the trick so far.
He also went away and worked on his action after the Ashes while the others were playing in the one day stuff, trying to get much more side on. Whatever he did it certainly seems to have worked; he seems reinvigorated and his pace was up a good 4-5 mph average over what he was bowling a couple of months ago. I'm pleased as Broad just seems to genuinely love taking wickets for England, and when he gets on one of those spells there's no stopping him.
Worried about the third seamer slot though. Obviously in time Stokes will be back to bowling more overs so it will take the pressure off slightly, but at the mo whether it's Woakes, Overton or Wood that plays, they seem to make more of an impression with the bat than they do the ball (which is practically nil).