FFF - For what it's worth there's an updated Thom 7 which is more useful than the older one that I've got (and I suspect you had too). CAP413 is undoubtedly better, I agree, but I found it rather dull.
Thom books 5 and 6 aren't needed either. Book 5 is mainly for the IMC exam (at least, I've done all of the PPL exams without needing a copy), and 6 is far too complicated for the trivial PPL Human Factors exam and the wrong one for the ATPLs (my instructor recommends "Human Factors for Pilots" by Green et al. for that).
Therefore it's only really books 2-4 and CAP413 - should be less than £50 second hand...