USC should theoretically be worth roughly 2x what pesetacoin is worth as there will be half as many total coins (as peseta.) It's a coin of importance because it was the first to introduce scrypt merged mining and other merged coins rely on it being kept up-to-date.

In reality, it's worth whatever someone will pay... you could always post an ad selling USC and see what offers you get. In the medium-term, it would be wise for the backers of USC and other chains based on it to get USC on an exchange.