I think that if Britney released her European bonus tracks (like Quicksand, Trouble, and Amnesia) the album Circus would re-enter the Billboard 200 and Digital Album charts. Maybe the songs themselves would enter the Digital Downloads, Pop, or even the Hot 100.

Do Somethin' from Greatest Hits: My Prerogative was originally only released in America. When she decided to release it in Europe to promote album sales, the song became a hit world wide. I hope Britney decides to do this. I bet SO many people would rush to Itunes as soon as they found out the songs were available in the US.