Patina vs. shine
Shine is fresh and new and it sparkles. Shiny catches the eye and it appeals to the neophiliac, to the person in search of polish.
Patina, on the other hand, can only be earned. Patina communicates trust (because the untrusted don't last long enough to earn a patina) and it appeals to a very different audience.
The old guy at the gym in spandex, taking steroids and brutalizing himself on the big machine--he's trying to be both and accomplishing neither.
Brands and organizations face the same choice. A book like Permission Marketing could be updated weekly, in a vain attempt on my part to keep it shiny. But that makes no sense, as the ideas in it are important because they've been right for a decade, not because they're new. That's what a new title is for.
The challenge, then, is to let your classics thrive precisely because they've earned the right, because they have a patina of quality--but not to rest on those laurels, but to get busy inventing the new shiny thing for those that demand it.