No. Coastal California is populated by Democratic voters, people who generally prefer high taxes and more (albeit of questionable quality) government services. SF is dirty because it has never had a Rudy Giuliani to clean it up — and the aforementioned residents would never vote someone like that into office.
(I grew up in NYC, and have been living in both SF and Oakland for the last four years.)
It's a bit unfortunate, but getting a substantially cleaner, safer SF would require a cultural shift away from egalitarian principles that are deeply ingrained in the city's DNA.
Note that while downtown Manhattan is approaching a dystopian Disneyland of tourist-friendly homogeneity, there are still parts of the city that are scary no-man's-land, you just don't see them if you visit or live & work in gentrified neighborhoods.
Back in the day, NYC was nice or nasty block by block, just like SF is today.
No it wouldn't. It would just require spending more money on public sanitation.
Of course if you let homeless congregate and don't provide the services to clean up after them the place is going to get filthy. But there are more solutions than getting rid of the homeless.