To suggest that someone break off a trip down the California Coast at Pismo Beach because it "is very urban" is a bit misleading. You aren't in Pismo Beach very long and shortly after it you are in rolling agricultural fields that are at least as nice as going north from Paso Robles. What's more, if you are unlucky and get hit by the headwind whipping down the Salinas Valley, you will be in for some very long days.
I would (and do) take the route that goes down the coast (through Big Sur, San Simeon, and Cayucos) to Morro Bay and then heads inland through hilly pasture lands to a main road (with a good shoulder) that takes you to the outskirts of San Luis Obispo (17 miles). From SLO, you follow a frontage road next to 101 into Pismo Beach. You quickly pass Pismo's downtown and within a few miles are in the town of Oceano, who's state park used to have a hiker/biker (described in the Kirkendall book). That hiker/biker site is no longer available but you can reserve a regular campsite for (around) $40/night, though you must do it in advance.
From Oceano, you climb a short, steep hill and go along a quickly developing Highway 1 eventually finding your way onto the main street of Guadalupe (10 miles), a town surrounded by agriculture fields. It seems every other store in Guadalupe is a mexican restaurant and I've had some great food there. After that, you head out into more remote agricultural fields and a golf course, seemingly in the middle of nowhere. Eventually, Highways 1 and 135 meet up and you follow 135 to Harris Grade Road, a 7-mile uphill and then a 4 mile coast into Lompoc (28 miles Guadalupe to Lompoc).
Out of Lompoc, I take highway 1 up a very pleasant, deserted, but gentle 18-mile climb followed by a straight bomb down to Highway 101. Thirty-five miles later, you are in downtown Santa Barbara. From there down, it gets quite urban and you have to ride on Highway 101 right next to semis and SUVs doing freeway speeds. Getting through LA is done using a nicely done beach bike path. From Carson to Newport Beach is a bit grim but after Laguna Beach the ride to San Diego is quite nice.
If you don't want to go all the way down to San Diego, I'd terminate at Santa Barbara and take the train back to SF or fly out of Santa Barbara back home.
Ray