I think what people are concerned about is the number of days driving you have in a row. The distances seem quite manageable to me. I also tried to keep things under 4 hours for us. However, most of the time we had a 'day off' in between.
Looking at your itinerary with the driving distances added in (thanks losfp!), I can see an opportunity to re-shuffle a couple of days, and maybe be able to make a couple of your stops a bit longer.
From Yosemite, you won't have to stop in Columbia, just drive straight through to San Francisco. You'll be seeing plenty of big trees and forest at Yosemite, so I don't think losing the state park there and big trees would be too much of an issue.
Also, you could either drive down the coast in 2 days instead of 3, giving you an extra night you could spend somewhere else. If you did this, you'd have to be choosy about your stops. Otherwise, you could stop at a halfway point for 2 nights. You'd still be able to visit Monterey on the way through the 1st day, and Pismo Beach (if that's really important to you) on the 3rd day. It might be of interest to you that while I was planning my itinerary for this September, I found out that it's not the right season for the elephant seals. You will see sea lions in San Francisco anyway at Fisherman's Wharf.
We stayed in Santa Margarita for 2 nights (not far from San Luis Obispo, which is pretty much exactly halfway between San Francisco and LA). We spent our full day there exploring Morro Bay and Montana de Oro State Park. There were some nice beaches there, interesting geological formations, and there are sea lions in Morro Bay too around the jetty area. We also did a morning horse ride at Madonna Inn. The horse riding was nice, but we were all blown away by the hotel! It would be a fun place to stay in San Luis Obispo (all completely over the top themed suites). We had morning tea after our horse riding, and the restaurant there was like a blinged out Miss Maud's
Other popular 'halfway' stops seem to be anywhere along the Big Sur coast, San Simeon (the kids might get a kick out of the castle there), and Santa Barbara and surrounding areas. We made a quick stop in Santa Barbara and were underwhelmed, but we didn't really get any further north than San Luis Obispo (we came in from the east instead).
We did the drive back from San Luis Obispo on a Sunday and traffic was terrible getting back into LA all the way from the Ventura area. We went via Solvang, which was cute and a nice place to stop for brunch. We also stopped in Santa Barbara, but were underwhelmed. Closer to LA, we did a detour via Malibu and the only thing I'd write home about there was the traffic
