I haven't read Heidi since I was a child but this blog post* by Leslie Wilson has inspired me to go back and look. I just remember it being a good story and I'm sure the subtext about poverty, and the way the poor are exploited by the wealthy, totally passed me by at the time. Leslie has an interesting perspective on the book, being half-German and having read it in German for the first time. This family background also informs her own books, Last train from Kummersdorf and Saving Rafael, both of which we have in the library.
* From An Awfully Big Blog Adventure - the ramblings of a few scattered authors.