The problem is that the LA area probably needs an insane amount of investment into its transit systems. What they have is nice, and the medium-term plans for more cross-connecting lines and the like are useful, but the area is so spread out that getting reasonable-frequency two-seat or three-seat rides between various locations is a very real problem (while having more than two transfers in a trip is going to weigh against using transit). The Bay Area is a bit better off (if only because development is awkwardly jammed into various corridors) but in the long run there's going to need to be much more expansion of the feeder networks in the LA area to really make CAHSR useful.
I think the thinking is that if you put in fast and frequent high capacity corridors, that those corridors will atract development and high denisty residential and commercial developments will estbalish themsleves around the stations. Thus in addition to serving structures that are already there (which is very difficult iof they are spread out) you are also catalyzing future development which will be more transit frienldy.
You can observe in places as diverse as New Orleans or Houston how a lot of stuff is being built or refurbished near light rail stops but a couple of block further away all is much more static. If you project a continuation of this develoment into the future, the percentage of people served by light rail will grow organically, even if you don't add further lines. But the adding of lines becomes necessary as the existing corridors run out of usable plots.
That's generally the idea, and very often it works (look at the DC Metro or the Vancouver Skytrain for examples). In the LA area, however, no small part of the problem is that there's only so much you can really hope to condense into some of these areas...and then you get into "around your ASCII to get to your elbow" situations where you have two parallel lines but no way to get between them , at least for a long time . There's also the fact that unlike DC and some other cities, there's not a single "easy" downtown area to point to in the LA area on the (relative) scale of some other cities.
 In most cases, a high-frequency bus option would probably be the shorter-term winner, but that's probably not a permanent solution in many cases.
 e.g. the Sepulveda Pass project presently does have a connection to LAX coming...in 2059.
Amtrak mileage to date: Somewhere between 120,000 and 150,000 miles...I /really/ need to run all of my trips through a calculator sometime.
...and no, I am not /that/ Anderson...;-)