Books with good graphics, eye-catching font and good quality covers sell more copies than those without. It's as simple as that. But designing (and choosing) the right cover for your book might be trickier than you think. It's not just about what YOU think reflects the content of your book - in fact, whether the covers reflects the content, might not be as important as you think.
The book cover is only package, nothing more, nothing less. And every package tries its best to stand out from other packages. If your book is set around a beautiful lake and there's an old man, this does not mean that you should put a lake and an old man on your cover. There will be thousands of covers like this. Forget your creative writing skills for a second and instead focus on creative marketing. What would make this story stand out visually? In what way would it differentiate itself from the other millions of covers on the market? What would your target market expect to see? If it's a romance novel you're writing, the cover SHOULD be romantic, but it SHOULDN'T be dreary and bum-numbing . If it's a political thriller it should be suspenseful, but it shouldn't be cliche.
So in short, yes, your target market does matter. You should keep them in mind when seeking the right book cover design; all readers have subconscious design, color and even typographical expectations when they're in the market searching for a book to read. Pay respect to these aspects. On the other hand, give them something new as well. That's why, whenever we design a book cover, we try to strike the right balance between what is "familiar" and what is "bold and innovative." That is the essence of a good, working book design. Happy searching!