I don't know whether it is still up to date enough to play.  His Benoni lines are much more tactical than the rest of his repertoire.  Playing his lines might require periodic study of recent games.  This is quite a break from the rest of the repertoire, which one could probably play for a decade on general understanding without following recent trends.

A great companion book to Palliser's book is Grivas' "Beating the fianchetto defenses".  Grivas' recommendations against the Benko, Grunfeld, KID, and Modern are very similar.  Grivas' book is a bit more current, and offers a more stable line vs. the Benoni that seems to fit the themes of Palliser's repertoire better than the line Palliser chose.