I was there for, hm, probably about four days. Which was certainly not too much, but it's not like London or Paris where four days will limit you to only the most famous of sights (at least if you're an avid museum-goer like me). SF isn't really a museum city, anyway - you're more likely to visit landmarks like the Golden Gate, or neighbourhoods like the Castro (the gay neighbourhood), the Mission (the oldest part of town), the Haight (the hippie neighbourhood) or Fisherman's Wharf (the old port), where atmosphere is at least as important as the actual sights themselves. One thing coming to mind that's less famous but quite impressive - near Fisherman's Wharf there's a WW2 submarine that you can visit, that was pretty cool.

Keep in mind that SF is seriously big, in terms of surface. Walking from one place to another will take a long time (I did it anyway, but then I had four days), even by car or public transport it might be further than you're used to. It's not like European cities or even Manhattan. Probably L.A. and really all cities in the Southwest are the same in that regard. There is a designed sightseeing route that will take you around the main sights of the city by car - it's forty-nine miles.

If you're in the neighbourhood, the City Lights bookstore on the way from downtown to Fisherman's Wharf is pretty awesome, and considering your love of music, you might like the record stores in the Haight and the Castro. The Golden Gate Park (which, confusingly, is nowhere near the Golden Gate bridge), starting right next to the Haight, is enormous and some parts of it are very nice, there's also botanic gardens and the like.