There's a points schedule on p26 of the UCI cross rules:
http://www.uci.ch/Modules/BUILTIN/ge...34593&LangId=1
Class 1 events get more points than class 2.

USGP is a series of cyclocross races, just like the Superprestige and the Gazet van Antwerpen. So you can earn UCI points and series points at the same time.

I believe (?) that UCI points determine staging for all UCI races, including World Cups and the World Championships. But it's more prestigious to win the World Cup points championship than the UCI points championship, because the World Cup is an international series and each World Cup event has a stacked field.