Aldiss, Brian W.
Book= VG+ or better
Intangibles, Inc. (1969), by Brian W. Aldiss. A collection of 5 novelets/stories.
"Since the Assassination" is original to the Faber 1969 hardcover. The rest originally appeared (from 1959 to 1968) - in Science Fiction Adventures (the British continuation), Science Fantasy, Magazine of F&SF, and Amazing. An American variant of this collection came out in 1970: Neanderthal Planet, containing 3 of 5 stories from this and adding a fourth novelet.
Some plot summaries: