Sorry this is late but I've been away.
I've also done Altered books but with ninth graders.
IMHO a theme is not super important. I let students
choose their own theme but honestly most make theirs
what I call a self-portrait. They just create spreads
about what interests them. they were a big hit and I'm
doing them again this year. If you're interested you
can email me off list or search the archive because I
spoke about these near the end of the school year.
you can see them at our site.