You don't necessarily need a car as hotel shuttles and regular bus services go to most of the major attractions. A rental car is handy if you want to go into the Hinterlands behind the Gold Coast. It's often cheaper to get a shuttle to Surfers than rent a car.
Make sure you buy a Gold Coast Tourist Shuttle Freedom Pass before you leave home. The Freedom Pass is reasonably priced at NZ$111 per adult for seven days and includes door to door transfers from Coolangatta to your Gold Coast accommodation as well as unlimited theme park transfers with Gold Coast Tourist Shuttle, and unlimited use of the Surfside Buslines network on the Gold Coast. You can purchase three-, five-, seven, 10- and 14-day passes. Not only do they offer convenience and reliable transportation but they are great value for money.