You'll want to be careful about the drive from San Simeon to Anaheim if it's on a weekday. You can hit major traffic snarls if you're headed through Los Angeles between 3pm and 7pm. And since the drive from San Simeon is a few hours, you might just hit that mess if you're not careful. You'll want to either leave San Simeon by 9am, or if you want a nice leisurely tour down the coast, stop for lunch in Solvang and for dinner in Santa Barbara. The Solvang/Santa Ynez area is a nice drive, and Santa Barbara is a great place to have dinner on the water. Leaving Santa Barbara around 7pm should help you avoid any traffic snarls further south, and will get you to Anaheim by 9:30pm or so.
Heading south from San Simeon, travel the 101 freeway and get off at Exit 146, Los Olivos, "Route 154" . Follow this through some nice countryside for about 8-10 miles until you hit Route 246. Turn right and this will take you into the danish village of Solvang, great spot for breakfast or lunch or window shopping. (You'll know you're there when you see buildings/storefronts with windmills). Back onto on 246 continuing west a few miles and this will get you back to the 101 freeway going south to Santa Barbara.
In Santa Barbara you'll want to head to the wharf/waterfront for a walk, and maybe a casual dinner at Santa Barbara Seafood right there on the wharf. There is also a trolley that takes you back and forth from the wharf to downtown Santa Barbara if you have time to look around.
Actually, Santa Barbara would be my choice for an overnight stay rather than San Simeon, but you may not be able to drive that far on that day. San Simeon's nice too.
Here is your exit for Santa Barbara!:
http://www.westcoastroads.com/california/images100/us-101_sb_exit_097_02.jpg