Unless they're maintained like a green lawn, grass strips will tend to be clumpy and hence a bit bumpy. Most of the weight is off the gear though when you're juddering along quickly - I'd say that it's easier on the airframe than you might think. A few points:
Wondai is grass with a bit of gravel - definitely NOT sealed. (Unless it's happened since December 2012). It is designed to be usable after plenty of rain though.
Archerfield 10R/28L is listed as gravel on the edges - must be under the grass, making it look like a narrower but completely sealed strip.
I flew over Kooralbyn on November 06 2013 and there were the big white Xs of closure at either end. Still looked like the best bet for a forced landing in that neck of the woods though.