Bump for update, just got back from trip, figured wouldn't hurt to share my impressions:
Redondo Beach: low-key, blue collar vibe. Marina here had a bunch of hole in the wall bars (very divey but beers were good & cheap). Place called Quality Seafood had amazing fresh seafood that they broil or fry right there, also very cheap. Beach was just OK, seemed like mostly locals.
Hermosa: didn't spend much time here, just walked thru. Long stretch of really nice beach homes, a few bars and big open beach. Not much else, seemed to be pretty low key as well.
Manhattan: had a blast here. Great bunch of bars and restaurants. Shellbacks for beers was good. Wahoos for fish tacos. Lots of volleyball type girls (tall athletic blondes). Locals were all very friendly and fit right in at night bar hopping. BEAUTIFUL homes along the water ("Strand").
Venice: VERY raunchy, but also a must-see. Mecca for bodybuilding & beach bums, but also seemed very artsy & hipster-ish (almost every girl was tatted up). Lots of crumby gift shops & bums selling goofy knickknacks, but still entertaining to see all of the characters. Weed also seemed pretty easy to get. Only walked through in the morning and was pretty skeeved out, so headed off to Santa Monica.
Santa Monica: Only here during the day, seemed pretty commercial & family oriented, lots of tourists as well. Great beach & fun town, can't comment on nightlife but seemed a little bit more upscale. Also lots of shopping and tons of girls all over.
Also drove by the touristy stuff like Chinese Theater, worth it to stop by but only for a few minutes. Ended up walking down some street in Beverly Hills that had a lot of open restaurants & bars, surprisingly not that $$$ and had a good time (mix of yuppies & hipsters where I was). Also went up Mulholland Dr for the view, also worth it to see LA all lit up.
Then left LA:
Santa Barbara: 1st impression was that it was kind of sleepy since my hotel was near the pier (just a bunch of stuffy resturants and boutiques), but then I found State Street ... FUN! Tons of decent resturants and very solid bars. They had some festival where people were throwing confetti eggs at each other ... which lasted all night. Very safe too, cops all over. Stayed out all night bar hopping, it's like a super glorified college town (obviously due to UCSB). Also drive along Rt. 1 thru Malibu was great!
San Luis Obispo: Seemed like more of a county town. Downtown area was small but had a bunch of decent restaurants and a couple of bars. Then went to Avila Beach, which was really nice but the town there was also pretty small and mostly for families. Overall had a good time, but very laid back (not much action), worked out well since I was still recovering from SB.
Carmel: BEAUTIFUL beach, BORING town. Basically just grabbed lunch, ate on the beach, and bounced. It's mostly art galleries & jewelery stores, seemed like where old rich people hang out. Think Big Sur was along the drive here, which as also very scenic, I recommend stopping off at some of the parks/vista points real quick just to get a good glimpse of the coast, it really is beautiful.
Monterey: Went here same day as Carmel, not much to see here either, two areas: Cannery Row & Fisherman's Wharf, both felt like tourist trap type areas. The aquarium was actually really nice (girl I went with loves sea otters to she treated). Bars & restaurants weren't all that impressive either, just OK, pretty quiet day.
Santa Cruz: Reminded me of a west coast coney island. Boardwalk has lots of attractions & rides, which attracts a lot of families but (surprisingly) there were a lot of girls my age (mid-20s) as well. Beach itself was pretty nice. I also LOVED the pier here. TONS of random, low-key bars and seafood spots. Got pretty trashed on cheap margaritas & shots, then ate some really great seafood for very reasonable prices. Just kept bouncing around until I got back to the beach, at which point I had to call it quits for the night lol. Also the pier is covered in seal.
San Fran: too much to list, staying near Union Sq is very strategic, lots of cool neighborhoods in walking distance but DON'T walk down into/thru Tenderloin, not necessarily dangerous but what a filthy & depressing place! Just tons of bums and garbage and human waste is EVERYWHERE. Just avoid, no reason to even cut through, go a few blocks over & you're fine. Did all of the touristy stuff the first day (golden gate, twin peaks, coit tower, wharf) so got to explore a lot. Cow Hollow along Union St, Filmore St & Chestnut St was great, got BOMBED bar hopping during happy hour. Great drinks for great prices, and the crowd was very cool & got along with pretty much everyone. Dipped into PAc Heights (I think) and it was nice too, less spots and more $$$. Little Italy was also VERY nice, I grew up going to Mulberry St in Manhattan every year, and I can say the San Fran Little Italy is just as good if not better than the one in NYC, it was VERY impressive.
Probably missed a bunch of stuff so I'll add to the update if I remember. Also have tons of pics if anyone is interested in any particular areas.
Thanks again for the advice folks!