Cut over on California 41
A couple of comments.
The first tour of Hearst Castle is at 8:20 am according to the Hearst Castle website www.hearstcastle.com, and takes around 2 hours including the bus trip up and back from the castle.
But don't drive south to Santa Barbara. The fastest route east is to go via California 41 -- head east from Cambria to Paso Robles, and then after taking a short dog leg north, you'll continue straight east across California heading to Lost Hills. At Lost Hills you can continue either on 99 or I-5 south until Bakersfield (you'll need to cut east from I-5 to get to Bakersfield), and then to CA-58 which goes straight east to Barstow.
It's not the most exciting route --- but a pretty good route, and the fastest and most direct. The computer claims its a 5 hour drive (without stops for gas or whatnot) to Barstow from San Simeon.
Seeing LA means getting into the city... and traffic
Hmm... there aren't very many routes, or any really good fast routes to head east once you get south of Paso Robles/ San Luis Obispo. As you head south, there are only a handful of routes which go over the coast range, before you get down to the LA area. And once you're in the LA area you'll be in the midst of BIG CITY traffic. Getting through LA can be a several hour experience at the wrong time of day...
Basically your routes look like
a) East from Santa Maria on California 166 to Cuyama (a small hamlet along the road) and then Maricopa, but traveling near the Carrizo Plain National Monument. The Plain is interesting, if you're into geology and plains wildlife (Tule Elk for example) -- but its a 2 lane paved state highway which winds through the mountains for most of the route. You will cross the San Andreas Fault in one of its more visible sections, but you need to know where to look to really make it out. And you'll be coming out in an old oil area near Taft (there's a oil history museum in Taft which I find interesting).
b) North from Ventura (or east from Carpintera) to Ojai, and then over the Coast range through Wheeler Springs and eventually out at I-5 at Frasier Park (near the top of the Grapevine grade). This is California 33 to Lockwood Valley Road. Ojai is an interesting arts community, and a nice place to stop for lunch, but again, this route is pretty much a 2 lane paved state highway which winds through the mountains.
(You could take CA-33 up to CA-166 at Cuyama, and head east on 166, but that's backtracking quite a ways).
Both of these routes take you through the coastal range of mountains, which sort of get short shrift around California -- not because they aren't significant mountains (peaks of over 4000-5000' in elevation), but because they aren't as large or spectacular as other mountains in the area which go over 10,000'. I've always found them interesting to travel through, since its pretty much the old California with native oaks and grasslands -- but its not very accessible, nor with significant towns.
c) Continue south of Santa Barbara through Ventura and take CA-126 to Santa Clarita, and then continue east and north on CA-14 back up to the Lancaster area, from which you can head east again, outside of the LA city metropolitan area. CA-126 isn't a major highway, and I've not driven all of it, so I suspect much of it is a 2 or 4 lane paved road. Santa Clarita is home of Magic Mountain theme park with many roller coasters. You'll also be passing past the Vasquez Rocks County Park, which has been used for very very many movies and TV shows as a backdrop (Gunsmoke, to Star Trek, to Bill & Ted's Excellent Adventure). You'll also pass close to Lancaster which is the home of several major aerospace facilities, including the Lockheed Skunk Works and is very near Edwards Air Force Base where many new aerospace vehicles are tested.
d) Continue south of Santa Barbara, through Ventura, and then climb up over the grade into Thousand Oaks and drop down into the San Fernando Valley on the outskirts of LA. From here you'll have to pass through just about the entire width of the LA area before coming back over the mountains on I-15 near San Bernandino -- which is at least a 90 minute drive at full interstate speeds. Add in traffic and it could easly be several hours at rush hour. If I had to suggest a route to do this, and to "see LA", I'd suggest hooking back north to catch the CA-118 freeway (6-8 lanes) at the northern edge of the San Fernando Valley, and then east to the I-210 "Foothill" freeway which contours along the northern edge of the LA basin. That will take you through Pasadena and east through Claremont and hook up at the I-15. That's probably the fastest route, since the 101 freeway through the valley is one of the busiest freeways in the world, and I've never taken it in daylight without running into significant traffic. If you have to go through LA during a work day (M-F) try to pass through in the hours between 9 am and 3 pm.