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If you really don't want to spend more than 4 hours or so a day 'in the saddle' then just the trip you roughly outlined initially (northern California to Yellowstone, to Seattle, and back home by way of the Columbia River Gorge and the coast) is a solid 2 weeks. Drives of 23+ hours are not recommended on either safety (none) or just pure enjoyment (even less) grounds. The Black Hills are flat out of the question, and even Salt Lake City would add an additional 100 miles (2 more hours or half a day). The other place I'd suggest that you cut back is going all the way to Seattle, rather just head from Yellowstone to Portland, which naturally has you driving down the Columbia River, and save 250 miles of driving. My route of choice from Yellowstone to Portland would be US-20/US-26 to I-84 and follow that to Portland, with the exception of using the Historic Columbia River Highway (US-30) wherever possible and hiking in to some of the many waterfalls along the way.

AZBuck