The book shows itself at the beginning of Douglas's unconsidered literary career. A screen writer, he didn't want to write books, but write books he did, given enough prompting and large amounts of small green pieces of paper. The book shows the writer's newness to the medium, reading in a rather uneven yet deeply comedic fashion. No pro writer would have put that book out, because you just don't structure a story that way, but Douglas was writing by the seat of his pants when he wrote the radio show which the book adapts, so he paces fairly close to the original story. What is very obvious from the beginning is that the man knew how to twist a phrase, tie it into knots, wash it, dry it, hide it in the bathroom, and in the end, throwing it when it became unidentifiable.
Douglas Adams also showed himself among the best futurists that the world has ever seen, if only because he knows that the engineers aren't in charge. He keen looks at how technology can go wrong proved prophetic to the years ahead, because new technology sure likes to go wrong.
On the whole, I feel that the book has aged well. There are some references to tapes and databanks, and other period technologies. The Guide itself is described as having a very small screen. And yet, mostly, you don't notice the technology at all once it gets going because the important parts of recently technology haven't change much. More importantly, the frustrating and annoying parts of technology remain the same because marketeers and engineers haven't changed very much. Dumb ideas remain dumb ideas.
You should give the book a try. It's a quick read and though a bit rough about the edges, looking at times as haggard as the original actors, once the characters start speaking, all that will wash away. The humor in it that works still hits the mark, assuming that you like British humor.