That depends on the customer segment you are targeting.

Over-complex design does not drive sales unless you're trying to send all your competitors down a dead end street.

Or, if you're selling "Enterprise Software". I've had to re-design things to be less simple, in order to make them more attractive to customers, and had my staff spend countless hours developing bells and whistles that impressed purchasing VPs in demos, but then were never used by the actual users.

Some customers will take "more features, and a busier looking interface" over "a simple, elegant design that actually does everything you need it to" every time. In my experience, these tend to be the customers who are not users themselves-- but, they often have the purchasing power over thousands of users.