Thanks for the trip report. My son, dog, and I love traveling the North Cascades Hwy. If you head back, explore up above Mazama where the highest driveable road in WA state is.
We (NW Overland Society) have done a couple of trips over there, and while there aren't any 4x4 trails it is a great place to go camping, hiking, fishing, and photographing. You're report has me considering when I'll head back again as it's very conveniently located (we live at the base of Hwy 20 in Mt. Vernon).
Thanks for the report!