Are you going up through the Catlins? The East side of the South Island is one of the last areas to get a feel for the way NZ was back in the early part of the 20th century. There are some beautiful waterfalls there, if you have time to see them.
Depending on how tired you want your arms to be, the Port Underwood Road from Rarangi to Picton is quite the drive. Lots of great scenic vistas and views of mussel farms. I don't know if the Mussel Pot restaurant in Havelock is still there, but it was good back when.
On the North Island, the 309 Road in the Coromandel area is a great ride, too.
I'm loving the RR. Keep it up!