Almost as long as I have been working to make the lives of software engineers better, people have been asking me how to measure developer productivity. How do we tell where there are productivity problems? How do we know if a team is doing worse or better over time? How does a manager explain to senior managers how productive the developers are? And so on and so on.
In general, I tended to focus on code simplicity first, and put a lower priority on measuring every single thing that developers do. Almost all software problems can be traced back to some failure to apply software engineering principles and practices. So even without measurements, if you simply get good software engineering practices applied across a company, most productivity problems and development issues disappear.
Now that said, there is tremendous value in measuring things. It helps you pinpoint areas of difficulty, allows you to reward those whose productivity improves, justifies...