We have used Sonlight all the way to high school level and I enjoy the variety in the cores - some focus on world history, others on American history, Eastern Hemisphere nations (a great core) and then the same again more indepth at high school level.
Whether you live in the USA or not, I would still do at least one year of American history. So many great books and movies are American and when you understand where they fit in, they make so much more sense.
Moreover, America is a political superpower today and when you understand their country's history, it helps you understand them as a nation.
(Are you beginning to tell that we don't live in the USA?)
Since I never studied America at school, I have enjoyed the American cores in Sonlight. Now I even know where most of the states are situated geographically (more or less!)
Likewise, if you are American, its good to learn about other nations of the world and I think Sonlight does a pretty good job of that too.