This is a very good question, and I would be curious what others do as well. We don't have any formal documentation for measuring but mostly conversations with Project Managers or Reviewers that are looking at products (plan sets/exhibits) provided by the AutoCAD staff. Through these conversations with Senior staff we can gauge which users may need more attention, I even like to do one-on-one check-ins with users, maybe there is a simple workflow they are missing that would help.
We also do monthly "Tech Talks" where I pick certain topics, such as a walkthrough/best practices with the Sheet Set Manager, Grading techniques with feature lines/grading tools, and use cases of current projects using corridor modeling. Even if a user picks up one "tip or trick' may make a difference with their daily work.
Another factor I have found is that users are not following established CAD standards by not utilizing correct templates or even following naming standards so if you can make sure users are starting off on the right foot, it should help a lot.
