I think the show is pretty scripted (or mtv at least tells the kids where to be and who to go see on any given day).
As far as the money factor, it's obviously been highly exaggerated for the cameras because they know that if there's anything MTV watchers like to see, its displays of obscene and ostentatious wealth (Rich Girls, My Super Sweet 16, Cribs, etc.) Also, I think some of the events, especially the "black and white" ball, might have been funded and partially organized by MTV and they just told the girls to invite people.
The high school the kids attend is probably your typical nice public high school in a heavily white, safe, suburban area. You could probably capture the same types of kids and the same interactions at a high school in say, Westchester County or in any of a number of Los Angeles suburbs.