I had been up to the top in a 4WD on a couple of occasions in summer - to fly down by Paraglider. But then one winter in heavy snow, I ploughed my way up on my own, overnighting in the small hut part way up.
Stayed at the Mt. Fyffe hut for a night before waking up for sunrise over the Pacific and the summit. Reaaall easy walk up (its graded for horses) with spectacular views of the larger mountains of the Seaward Kaikouras, as well as to Kaikoura itself.