Most of my clients (who have marketing but not design backgrounds) want that "wow" factor when they see the first mockups. By easing into the designs I felt like I lost that.
As a designer I realized I wasn't just delivering a JPG, but a design experience. My clients seemed to equally enjoy putting their mark on the design and imaging the same "wow" factor their CEO would feel when they saw the latest iteration.
So, while I love this process for personal projects or for companies familiar with the design process, for the average marketing team I'm still going full color mockups.