Regular rail will ultimately have to replace a great deal of road traffic, and having the HSR backbone for longer-distance regional travel will make it far more useful, and enable its construction. Light rail should be built, and I think it will be. But it is a much longer-term (and far more expensive) proposition.
For example, consider the planned expansion links of the Metrolink system in Southern California:
http://bit.ly/NLze6ITo lay just 9 miles of light rail track from downtown San Bernadino to the University of Redlands (the "Redlands Corridor"), the estimated cost is around $700 million
http://sanbag.ca.gov/projects/redlands-transit.htmlAnd it would take around 10 years to build
http://sanbag.ca.gov/projects/redlands-sb-rail/Scoping_Presentation_04-24-2012.pdfAccording to the latter link, that effort began in 1989 with a voter-approved measure, after which they started buying right-of-way. Now, 23 years later, they still haven't laid a single mile of track.
All that, for 9 lousy miles in San Bernadino, which isn't as built-up as central LA.
Now imagine building all the proposed expansion links in that wiki article. Then imagine building far more than that, to really get the cars off the road. How much would it all cost? In the trillions, to be sure. You think it's hard to raise $68 billion? Try that. And it would many decades, if not a century, to build it.
To be clear, I DO think we need to do all of the above, and more! But as a practical matter, I don't see how a comprehensive light rail system could get built in Southern California any time soon. With such long timelines and huge costs, there has to be a large degree of federal support, and federal support is more oriented (sensibly, I think) toward projects that connect major cities than building within individual cities.
So, I think when you put it in context, the SF-LA HSR and its price tag looks pretty good. It can actually get done, with a substantial amount of federal support. By the time it's operational in 2028, I expect that flying from SF to LA will be very expensive with very limited service. It won't be anything like today. If we don't have a rail substitute by then, the economic damage to the state could be devastating.
As for your claim that light rail makes more sense than HSR in energetic terms, I am unconvinced. Let's see your data.
