My main issue is the way they are going about it, which is a highly politicized construction process along with some really out-of-order prioritization.
It would be much better to start with the low hanging fruit, like grade separation and electrification of Caltrain. That line would benefit immensely from some major upgrades, such as longer station platforms. To be fair, the most recent round of upgrades (ctc, quadruple track sections, new rolling stock) have been very well done.
According to the WSJ, 6 million people per year travel between LA & SF via air every year. I can't find highway numbers, but I gotta believe it's about the same order of magnitude, if not higher.
Improve BART, VTA light rail and CalTrain (in the Bay Area), and I suspect it will have a much larger positive impact on the lives of more people.
All of the above need to be done, both will have a positive impact of even more people.
I don't know, it just doesn't seem like a very compelling argument to me. The state doesn't have unlimited resources. Spend the money where it will do the most good.
[1] http://www.hsr.ca.gov/docs/newsroom/fact%20sheets/Good%20for...
[2] most recent month with available statistics, lots more data available here http://traffic-counts.dot.ca.gov/
In highway terms, that's a significant reduction. A reduction on the order of 1-3% (it depends on a number of factors including number of lanes, and distance between exits) can get you from LOS F traffic (stop & go) to LOD C/D traffic (heavy, but moving traffic).