FWIW, outside of Kentucky, USC would probably be my second collegiate team in college football. I've always enjoyed watching them play.
To be fair though, Mike Williams probably isn't the best example given he sat out a year fighting the NFL trying to get drafted.
I don't think Sanchez is quite ready right now, and a full year with a clipboard would likely be the best option depending on who drafts him. I think he is better served to come out this year than wait until next when he is going up against Sam Bradford and Tim Tebow, among others.
Right now he has the chance to chase Matt Stafford for the first overall pick and possibly be a top ten pick. Next season, who knows what might happen.