Thinking of rebuying the Harry Potter books. I remember nothing from the fifth and sixth books and only ever saw the movies for the last books. Plus it's been upwards to twelve years since I last read them.
You definitely should. Just watch out for spoilers. Harry Potter is seriously fantastic though, one of my favorite series of all time. You should go through and read the whole series in order starting with book 1.
I wouldn't buy them if I didn't intend to read them. But I doubt there's anything that can be spoiled unless there's some major spoiler in the seventh book that somehow never made it into the movies.