Second (and more) languages are definitely valuable for the US -- having immigrants living in the US with fluency in their heritage language as well as English makes it easier for US companies to do business in foreign countries, and domestic people learning foreign languages helps as well.

I tried to find stats on the net costs of illegal immigrants resident in the US, and really couldn't find anything conclusive. The best information seems to be that they could impose slight net costs on some communities, but that it's a relatively minor amount relative to the size of budgets.

I definitely wouldn't say California's problems are mainly due to illegal immigration. I'm just curious why it is so much more of a political issue in some states than others.