Look at the implication of the title, Mr. Sammler's Planet. It implies that because he sees things from his own enlightened point of view, that he also has a kind of subjective authority. Not only does he know a lot about life, having lived through the Holocaust, but also, he understands that other people in his community are privileged, so they don't have to face the true gravity of life and its various plagues. He himself understand these things through suffering, so his experience of the planet is all his own.
When people herald the luxurious life of the wealthy, that's when Mr. Sammler finds himself most grumpy and critical. It isn't luxury that serves the human experience, but grit, he feels, because luxury is temporary. His point of view is that as a person suffers, they grow, and by spoiling one's self with money and luxury, one becomes less adaptive. Then, if the world falls apart like it did for him in WWII, they will be too entitled and morally weak to adapt.
Another way of seeing the plot is that Mr. Sammler struggles to reintegrate into society because PTSD and real suffering prohibit him from accepting the pleasantries and play of social situations. He doesn't see the value in pretending that life is nice or enjoyable, but partly because his own life is tormented by the unimaginable pain he suffered. One might say Sammler suffered the archetypal maximum, losing everyone he knew and loved in a horrific war and genocide.
