Isn't SF infamously a SFH zone that makes no sense? If you razed the whole city and rebuilt it like Manhattan, you wouldn't have 25% more inhabitants, you'd have 25000% more. And if you improve public transit (I heard BART is some that's pretty good by American standards but not by European standards?) you can drastically widen the area that feels like the core city (just take a look at Berlin which I'm familiar with) giving maybe another 1000% multiplicative increase.

Every time I'm in Berlin I love the public transit system there. I think that's because they have a relatively dense network of lines through the city center, and the trains run every 4-5 minutes which means you don't have to check the timetable before going to the station, you can just show up. I haven't visited London or NYC though. I know some cities with more modern train signaling have trains every 1-2 minutes so there is basically always a train at every metro station.