Does it actually have to be "on the coast"? Do you want something different from things you can see easily from home (cities, historical areas, beaches, and WDW)? How much time do you have and how much driving will you want to do? What about CA interests you -- it's huge and diverse. Oregon's coast is actually more interesting, and the Olympic National Park and Seattle area is wonderful.
I'd suggest seeing some of the natural wonders out there (which does include the Big Sur area) -- like Yosemite, Death Valley, Lake Tahoe, Redwoods/Sequoias, etc.