Drew, as nobody has answered your question I will do my best to give you a guide. I was a regular on the Pikowhai/Matata beaches up until five years ago, without a doubt one of surfcasting's premier locations.
Most of the beaches in the area are accessible with 4WD but local conservation groups were trying to reduce some of the places where vehicles gained access to the sand. The area is a known habitat of an endangered bird, I think the dotterel. You will still find plenty of areas you can fish with your 4WD but for choice I would have the Quad every time.
Many of the local anglers went over to quads and kept the 4WD off the beaches. It was a widely held point of view that as there is a road just 200 to 300 meters from the surf, there was no real need to have a large vehicle on the beach. I can also say if you have issues with your vehicle after dark, you will have problems finding help.
I am not sure I would like to tow a Quad all the way to the Bay of Plenty and as there are many kilometres of access for vehicles, I think I would just rely on your 4WD.
As an aside, at this time of the year those beaches are usually on fire. Never stray far from your rod, the next take could easily be a double figure snapper or a nice large ray. I have also caught Kingfish from the beach at Pikowhai.