This is one of the most eloquent breakdowns of a website redesign I’ve read. You can read the entire post on UsabilityPost.com.
A redesign is a symptom of a disease. A good design works to make the thing perform well and to communicate how it works to the user. It’s an expression of function. A well designed thing is beautiful to us precisely because its design is optimal for its purpose—its form is in harmony with its function.
A good design doesn’t need a refresh or a redesign unless the function dramatically changes. If the changes are subtle, the design should be able to accommodate them effortlessly. What we’re seeing though with website redesigns around the Web isn’t a change in function, but a change in style.
The cause of a redesign is an imbalance—a strong focus on style over substance. By focusing on style, you give way to trends, and by their nature, trends come and go. When you imbue your design with the latest trend you sentence it to death. As the latest aesthetic fancy flies away, it will carry off with it that which makes your design so appealing. It will become boring and old, and a redesign will be in order.