One of the primary traits of a good developer is a strong desire for excellence. If a developer is willing to settle for a mediocre and boring design, then that is some (perhaps small) evidence that the book may contain mediocre and boring content.
Anecdotally: At the TechWeek Chicago job fair, there was a very high correlation between booths with good logos and graphic design and interesting people behind the booth. All of my good conversations were with people at the well designed booths.
EDIT: This is especially true since we are expected to pay for the book before we get access to it. This means that we cannot judge its quality in any holistic way, but must do our best to pre-judge its quality through various social signals.
I personally go for things that have bad design. Like slackware linux. I associate bad graphic design with great software. I love seeing a great science fiction novel wrapped in a generic illustrated cover. It seems more quirky and personal to me. I think good design can be bought, so I distrust it. I really hate it when the packaging is slick, with a perfect logo, and a perfect website, but the product is terrible. Like you were fooled into buying it. It happens more often to me these days because good graphic design can be bought, or copy-pasted.
I tend to agree with you, but it's possible the places with budgets to allow for high-quality graphic design and production (let alone conference attendance) also have budgets that allow for the salaries high-quality people often demand.
Anecdotally: At the TechWeek Chicago job fair, there was a very high correlation between booths with good logos and graphic design and interesting people behind the booth. All of my good conversations were with people at the well designed booths.
EDIT: This is especially true since we are expected to pay for the book before we get access to it. This means that we cannot judge its quality in any holistic way, but must do our best to pre-judge its quality through various social signals.