I'm pretty sure those 50% bonus status points are like the other spend-earned status points in that they are not quite equivalent to status points earned by flying on AirNZ metal. Remember that a portion of points to attain status must be from actually flying on an AirNZ aircraft. For example to move up to Gold Elite requires 1500 status points of which 900 must be from flights. Spending earned points and 50% bonus only help with the other 600 points.