Calling the SP depot "undersized" implies that it is fully utilized now, which it isn't. Much of the depot is vacant or underutilized, and even the portion in use isn't generally crowded. Busy, yes--one of the busiest in the state--but crowded or stretched beyond capacity, no, not even close. Add a bus terminal, a couple of restaurants and a gift shop, and who knows?
SORD originally advocated for maintenance of the original rail orientation and station position, but the city decided that the "Sacramento Northern" plan, one of four proposed plans, was the best one, and SORD signed on--it wasn't their idea.
Here's the city website with more background:
I'm not sure what the point of the big triangular shed is either, personally I'm hoping that gets value-engineered out in favor of sheds closer to the current style.
About keeping the depot building where it is and building a new station, call me cynical but if the past is any indication of the future the station would sit vacant, a "homeless person" would start a fire inside "to keep warm" in the middle of August, and we'd have a parking lot for a couple of decades anyhow.
I think you may be overestimating the amount of authority and power that preservationists have in Sacramento, which is pretty minimal. At best it's like fighting a holding action.