I've done death valley twice over thanksgiving though it was about 10 years ago. For Racetrack we (two vehicles are always safer) brought a CO2 tank and dropped the tire pressures down to 20 PSI. This smoothed out the washboard and we were able to cruise at a pretty comfortable speed as the low tires absorbed the washboard and kept it from transferring through the suspension and into the vehicle. On the return trip we stopped just before the paved road and aired the tires back up. You could always use an air compressor, but the little ones are super slow and may even burn out before all the tires are filled again.
I don't remember what other canyons were called but we went to and saw many of them. I don't think I ever needed four wheel drive on any of the dirt roads I was on. Though I did usually engage it just because I could.