Although it is usually represented as a simple comedic science-fiction story, Douglas Adams used The Hitchhiker's Guide to the Galaxy as a satire on modern life, much like Swift's Gulliver's Travels. Many aspects of the story echo current-day issues in England, like the impossible bureaucracy of the Vogons or the position of Zaphod as figurehead instead of having real power (the Royal Family).
"I think the ship's brand new," said Ford.
"How can you tell?" asked Arthur. "Have you got some exotic device for measuring the age of metal?"
"No, I just found this sales brochure lying on the ﬂoor."
(Adams, The Hitchhiker's Guide to the Galaxy, Google Books)
Just like in reality, sales is important, and so a possible science-fiction explanation for the newness of the ship is replaced by a sales brochure with glossy photos and ad copy. Sometimes, a new spaceship is just a new spaceship. If there is a specific subtext, it could be boiled down to read: "Life is often absurd; we have little ability to cause great change; instead, worry about yourself, your own happiness, and the effect you have on friends and family, because they are more important to you than any world events." (subjective interpretation: Belarafon)