It seems to me that you have a choice to either do the mountain route, taking in Tahoe, Yosemite, and perhaps Sequoia. Or the coastal route, doing the Oregon & California coasts, including Big Sur. Tough, tough choice. Though you
could choose one on the way down and the other on the way back.
As much as I love Yosemite, I'd probably choose the coast for a road trip. Do US101 all the way down the Oregon coast, and continue down the California coast past Mendocino, all the way to San Francisco. In northern California, you'd hit all the major redwood forests. Redwood National Park is supposed to be great (never been), but I personally think that Humboldt Redwoods State Park is fantastic! It might be fun to hit both, and tell us which you think is better.
At Riverdale, I'd break off onto Highway 1, to hit Fort Bragg and Mendocino. Mendocino is a wonderful coastal town that may remind you of New England. They grow great wine in the area; nearly as good as Napa. I'd then continue down Highway 1, stopping at Point Arena, and for sure at Point Reyes National Seashore. Probably elsewhere along the way, too.
This route will then take you to San Francisco; another one of my favorite towns. But it's an urban experience, so you can decide how much time you want to spend there.
Next stop, Monterey; my home town, so I'm biased, but a wonderful place to spend at least a couple days. See the Aquarium; 17 Mile Drive; Asilomar; Cannery Row; Point Lobos; I could go on
After Monterey,
definitely take Highway 1 south down the Big Sur coast. Stop at Big Sur, Pfeiffer Big Sur State Park, and Pfeiffer Beach. Have lunch at
Nepenthe's. In any case, enjoy one of the most breathtaking drives in the country!
When you get down to San Simeon, you could tour
Hearst Castle. The opulence is amazing! But if you want to go, book a tour in advance -- they sell out.
After that, you could stop in Santa Barbara a couple of days; also a delightful place. From there, you're only a couple hours away from
Disneyland.
And then, on the way back, you can do the mountain route to Yosemite. If it were me, I'd probably take US395 up the Owens Valley, with dramatic views of the high Sierra Crest. At Mono Lake, stop to see the tufa displays. Then go east on CA120 into the Yosemite high country, ending up in Yosemite Valley. On the way, make sure to stop at Olmstead Point, which has breathtaking views down Tenaya Canyon to Yosemite Valley.
Anyway, that's just me.
-Bob