Well, there has been a lot of debate regarding this topic. I believe that good content should be well presented to the end-user. When you create a friendly visual environment on your website I am sure users would stay in it for a while and maybe browse new pages or even click on one of your ads, Whereas a very basic page gives the user a feeling that you (the site owner) didn't invest much or careless about the visual appearance of the site and this may lead to a user exiting your website promptly.
These days it's all about looks.. and the design of your website plays a big role in your overall earnings. Although content is the key factor in the business, how many people out there actually don't judge a book by it's cover?