For anyone reading this thread in the future and finding it of interest, here's our final-ish itinerary:

Day 1 - arrive SF lunchtime, taxi to city. Overnight SF
Day 2 - sightseeing SF. Overnight SF
Day 3 - sightseeing SF. Overnight SF
Day 4 - pick up car am. Overnight Monterey/Carmel.
Day 5 - Explore down 101 30-40 miles, turn and drive to Yosemite. Overnight Mariposa
Day 6 - sightseeing Yosemite. Overnight Mammoth Lakes
Day 7 - drive Death Valley. Overnight Death Valley.
Day 8 - sightseeing Death Valley. Drive Las Vegas. Overnight Las Vegas.
Day 9 - Sightseeing / Shopping / Rest and Relaxation Las Vegas. Overnight Las Vegas
Day 10 - Sightseeing / Shopping / Rest and Relaxation Las Vegas. Overnight Las Vegas
Day 11 - Sightseeing / Shopping / Rest and Relaxation Las Vegas. Overnight Las Vegas
Day 12 - drive Grand Canyon. Overnight Grand Canyon.
Day 13 - drive to Flagstaff-Sedona-Prescott Valley-Ash Fork-Kingman. Overnight Kingman
Day 14 - drive Mohave-Joshua Tree-Palm Springs. Overnight Palm Springs
Day 15 - drive LA. Overnight Newport Beach
Day 16 - Sightseeing / Shopping / Rest and Relaxation. Overnight Newport Beach
Day 17 - Sightseeing / Shopping / Rest and Relaxation. Overnight Newport Beach
Day 18 - Sightseeing / Shopping / Rest and Relaxation. Overnight Newport Beach
Day 19 - Sightseeing / Shopping / Rest and Relaxation. Home to UK

It may appear that we should stretch out a few of the one nighters to two nights but availability of accommodations don't work out that well and, with couple of kids possibly getting road weary and looking for some action rather than beautiful scenery, I'm mindful that I've only one vote in the car!

Any comments or suggestions or advice welcome!