Minnie Water does sound nice (was just reading up about it), I love spots that are a bit secluded. Camping the the NP looks good there. Washpool / Gibraltar NP also look interesting.
Clarence River sounds interesting too - just found out about the Clarence River Wilderness Lodge which sounds like fun, though we don't have a 4WD.
If anyone has recommendations for where else might be good to camp on the Clarence River, let me know