There is no optional LDW in NZ and there is no insurance to decline

The vehicle is insured and covered against damage, though unless you take out Accident Excess reduction or Max cover, there is quite a high accidental damage excess which Amex should cover

Excesses are

NZD 3450.00 (incl GST) for the economy manual, compact manual, compact auto, intermediate auto and fullsize auto car classes,
NZD 4025.00 (incl GST) for the premium wagon, 4WD, luxury 8 seater, luxury sedan and premium 4WD car classes