San Fran day trip - Yosemite, Napa, Muir woods, or other?

I am flying in from Sydney to San Francisco, late April. I have four days to myself to enjoy however I want (woohoo), before meeting friends to continue on for another day in San Fran, then on to Chicago. I've been there once before and covered Fisherman's Wharf, downtown, some great bars, a Giants game, the trams, and awesome chowder. What I'd like to take in this time, would be the more beatnik-y North Beach sites (Vesuvios, Citylights bookstore, etc), the vintage neon signage/old Lenny Bruce, Woody Allen stand-up venue areas that looks like it's along Columbus, as well as just generally wander, and see another side of San Fran. When my friends arrive, they want to do Pacific Heights, Haight areas, and Lombard Street, so they're covered also.

BUT, what I'm thinking is, I spend my first 2 days on a day trip, then head back to town for the other two, to cover the above, and be in town for my friends' arrivals. Yosemite really appeals to me, but there are a lot of great looking options like Napa, Muir Woods, etc – I'm wondering if that's the best option? I'm in my mid 30's, female, average fitness, enjoy natural sights, walking, good food/drinking, cool bars, quirky Americana, chatting with locals – not that into shopping or clubbing.

My thinking is this:

– Not to sound arrogant, but we do have a lot of really beautiful wine country in Australia, where I'm from, and I'm not sure I'd be seeing better there – but we definitely don't have a Yosemite.

– I've read that it's apparently good timing to see Yosemite, as the waterfalls are full, and there is access to the Sequoia area

– A downside is Yosemite is further away (4.5 hours each way I've been told), and I'd do it through an organised company (Incredible Adventures – anyone used them?) so that's less cruisy and more doing what a group want, rather than just me – not a terrible thing though, I'm sure. I'd do a two day tour with a stay on site overnight.

Any thoughts?...