The road from CHC to ZQN is pretty but it is not dramatic and mostly boring rolling countryside. Definitely not worth it in the winter (marginally worth it in the summer).

During winter the North Island is much better choice unless you really need world-class skiing. A lot better weather North of AKL, and if you must have snow there is always Rotorua. Plus you avoid the not negligible chance of being stranded for a day or 2 in the south island.