I took a tour, since access to the spit is otherwise limited to the first 6km or so.
It was well organised and comfortable, in the company's custom-built 4WD buses based on Bedford truck chassis.
Operator: Farewell Spit Eco Tours (www.farewellspit.com)
As I write this (2007.12.09) that's me in the orange jacket, in the photo on their front page.