Hello and welcome to the RTA forums !
As you are travelling in December it is unlikely you will be able to cross the Sierras on CA120 [Tioga Pass] to get to Yosemite from 395. You will also have to carry snowchains and may have to use them in the event of a storm.
You could with your time actually drive a complete loop from SF or Vegas depending on the best flight deals and see the west coast as well as Tahoe. Heading south down the coast to Cambria and then inland direct to the Grand canyon, [or perhaps with an overnight stop] stay at the canyon and then head to Vegas. From Vegas you could drive across Death valley and then up to Lake Tahoe and then US50 and down to Yosemite from the west side. If the pass were to be open then you could take the Tioga Pass but it would be unlikely at this time of year even though it happened recently.
You have the tall coastal Redwoods which you can find some in Muir woods north of SF among other places, or you have the giant Sequoia trees in Sequoia NP or in Mariposa Grove in Yosemite. It's impossible to know what the weather might throw at you but it can be a wonderful time to visit the mountains.