Bob has all the gory details I'm sure; all I've seen is the Draft EIR. But yes, making LAUS run-through (at least in part - it wouldn't be ALL of the tracks) definitely would help. While removing the need for reversing is helpful, it's more important that access to/from the south (toward Orange Co. and the 91 line) would be quicker and more direct than it is now. Among other things, reduced locomotive emissions due to shorter distance run and less accel/decel.

Admittedly, it would not help Amtrak long distance because those trains all terminate at LA, but again not all of the tracks would run through. And there are only a couple of long-distance Amtraks a day - insignificant compared to the other traffic.

One wonders why LA was done as a purely stub-ended station in the first place. At the time cost was almost probably an issue and the operations of the time most likely worked fine without run-through. No longer true; in the olde dayze there weren't any commuter trains. If you look at the number of train operated (including all the Metrolink stuff and switching/deadhead moves) LAUS is probably handling more trains per day now than it did at its "peak" in the 1930s-40s; if not, it's very close.