I read Jerry Spinelli's sequel to Stargirl entitled Love, Stargirl. I liked it, not loved it. I'm not sure that my students would love it. Stargirl seems fairly immature in some respects--I guess I expect more from a high school student. Stargirl has a junior high mentality. I don't think this book would be as appreciated by those Stargirl's age. Students in the sixth, seventh, or eighth grade would enjoy these books more than other age groups.
I do enjoy Stargirl's perspective on things--especially in noticing the little details in life. She pays attention to things most of us are too busy to even notice or care. I think this theme is more prominent in the first book; however, there are plenty of examples in book two.