The problem with air travel is throughput. There are 6+ million trips between SF and LA per year, and any significant increase either replaces other flights or requires another two airports in SF/LA, which ain't cheap.
HSR between LA and SF would be able to handle 15+ million people per year, on top of providing routes between other cities in CA, some of which don't have anything except for bus/car routes, and it would also free up capacity for more long distance domestic and international flights.
http://cahsr.blogspot.com/2009/10/la-sf-nations-second-busie...
HSR between LA and SF would be able to handle 15+ million people per year, on top of providing routes between other cities in CA, some of which don't have anything except for bus/car routes, and it would also free up capacity for more long distance domestic and international flights.