What is that one screen you see regularly on WordPress, but might not have customized so far? Yes, the dashboard. I have been using WordPress since long now myself, and very rarely have I seen someone spending time changing things on the dashboard. I think that is because people care more about what readers see, rather than what they see on the dashboard. However, the dashboard, in generally should be one of the most productive and useful screen on your site.
One of my favorite things about the admin theme with WordPress is the new Dashicons icon font. It brings a sense of standard and uniformity to dashboard icons with its distinctive look and vast array of icons for theme and plugin authors to choose from and use with ease.