Hey
@dhb10 this is the correct forum this time--well, close enough!
The one thing that gives me pause is that you aren't crazy about New York. People in NYC and LA have extremely strong feelings about their cities and many could only ever imagine living in one or the other. If you are truly an LA person and not a New York person, maybe just maybe you could keep USC in the picture. Caveat though: I am worried that you could be rationalizing your desire to go to USC by saying you're lukewarm on New York. If you could see yourself tolerating New York for four years, I think you should go there.
But you aren't asking which one to go to, rather how to ask USC for more money. I have no experience in these matters (and none at all with USC) but the typical advice seems to be politely asking via email. Personally I think it would be most effective if you could frame it with how it would affect your decision. If you would choose NYU as things stand, but would prefer to go to USC if costs were equal, make sure that Los Angeles knows that. (Obviously don't say that if it ain't true.)