The current Mission Bay and South Beach stuff seems to have gone really well.
Leaving Haight, Noe, etc. with the Victorian character would probably be enough to preserve SF's historical features.
I'm not really sure about increasing density in "suburban" SF (Sunset, Richmond) -- it's already 2-3 story apartment buildings and townhomes, so the next jump is up to 5 or so, and it's not very well served with transit now.