Hello all
Of course this is all a matter of opinion, but I would like to add my five cents worth:
Endgame Books: I would lean towards either Keres (PCE) or Dvoretsky's Engame Manual instead of Averbakh.
Middlegame: I would certainly not have the Silman book and probably not the Keres + Kotov book either (I bought that in 1973 for R1.10 !). A really difficult category but I would stick my neck out and pick Pachman's trilogy Complete Chess Strategy and Nimzowitsch's My System.
Games Collections: How can Fischer's My 60 Memorable games possibly be left out? The Nunn book is really good, but I would have preferred Secrets of Grandmaster Play by the same author (I have both). Serious contenders would be - not Chernev's Instructive Games which really is not in the same league - but Timman's Art of Chess Analysis or Speelman's Best Chess games 70-80.
"And Because" : I really cannot agree with the Fischer-Spassky book. The book was produced in a hurry to climb on the bandwagon of Fischermania at the time and is pretty skimpy on analysis. Timman has apparently written the definitive book on the match (which I do not have).
The other book can only be Polugaevsky's monumental work Grandmaster Preparation, part of which covers the birth of the razor-sharp Polu Variation of the Najdorf.