There are ALL kinds of reasons why good design matters but I am only going to concentrate on one reason today--ITS ESTHETIC APPEARANCE.
Look at the cover on Alexander Delchev's The Modern Reti An Anti-Slav Repertoire. The Art Deco movement of the 30s was "modern" for that time, and in its own secretive way it has still survived, especially when someone wants to claim an "objet d'art" as "modern." This can be aided by a typeface such as, what else?, "Art Deco." Of course there are variations of this face, one designer is not satisfied with the work of another and changes it... yet often the FIRST one is the one with the name "eternal" recognition.
Over time I have seen thousands of chess items in all kinds of packaging. Most of it is average-looking. However I want to recognize Kalojan Nachev, a Bulgarian, with the work he has done on Delchev's book. (For animation, commercials, music and so on check out http://3dust.com/ you will be floored and you KNOW the cost for their productions would be 10% of the cost for junk produced over here--unfortunately [BTW, I am rereading "Hey Whipple Squeeze this," so I am not making this up.]) The type and the "spotlight" style background, plus the color yellow is wonderful to behold. The chessboard and diagram is always a tough issue because there is so darn much "stuff" going on. I might've changed the color of the board and pieces because browns seldom interact well with blues--the pieces, fine. At any rate, the Chess Stars line of new books beat, on average, anything put out by Gambit, Everyman, and Quality. It's not that UK designers don't have skill, it's just that when it comes to chess covers it seems... like they have no skill.
If one looks at a Batsford catalog for OTHER (non-chess) books, the difference is gargantuan. You wouldn't think they came from the same company (and probably don't). When it comes to chess design it's hard to know what to say. Sometimes it should (?) be abstract, other times, it should explain (?) the book. Some of the worst cover designs in chess come from New in Chess. Even the interiors often look sterile and austere. But maybe this formula works for them... but one has to wonder, "If it were done with more artistic skill, would sales be even better!?"
This is a topic which can go on for a long time... but I won't.