Just a comment. Any way you can start out in SF, then drive to LA? Las Vegas is only a 4 hour drive

We ll be spending a week in LA then driving to SanFrancisco, staying in the bay city for a few days and then heading to Las Vegas. We hope to do the San Francisco to Las Vegas trip over two days with lots of stops and a stay overnight -
Do as tomfuller suggests if you haven't already done the coast drive on the way up from LA. Otherwise, there isn't anywhere along the main routes to LV that are stopover worthy. You could loop over to Yosemite, take a peek,and continue south thru Fresno quality accommodation berlin to Get back to Hwy 99, but it would depend on weather and finding accommodations. You may be better off just driving the 10 hours straight to LV.
But where are you going after Vegas? Is that the end of your trip? If so, consider dropping your car in San Francisco and flying to Las Vegas. It will save you HOURS of tedious driving. Plus driving down the central Valley in Feb can be so foggy it is dangerous. There are cheap airfares SF on Southwest which is a terrific airline but doesn't show up on kayak/orbitz/etc.
I agree with both janisj and MichelleY. If you have already traveled the coast, just go down I-5 and cross over to Rt. 99 wherever you want to to get on Rt. 58 at the south end of Bakersfield. If you are very tired, the only place I would stop for the night would be Primm Nevada at Exit 1. (42 miles from LV). Buffalo Bill's is not as nice as Las Vegas but it is better than getting lost in LV on your way to a hotel.
If you've done the coast and would like to see Yosemite, take I-80 out of the Bay area over to Placerville, wind your way down SR 49 through the Gold Rush country quality accommodation berlin and take SR 120 into Yosemite, drive to the Valley, quality accommodation berlin do a drive through then exit on SR 41 into Fresno. At that point you'll probably be ready to stop forthe night. Next day SR 99 to Bakersfield, SR 58 to Barstow and I-15 into LV.
Just a comment. Any way you can start out in SF, then drive to LA? Las Vegas is only a 4 hour drive from LA, but to get there from SF you will have to drive south again after having driven north to SF and there is nowhere worth stopping quality accommodation berlin unless you can get to Yosemite.