To your original question - I confront myself with this kind of question periodically, several times a year, usually when I am reviewing how my overall system is working. I tend to keep my QS-obsession to myself, so I really don't hear from others about it. I think QS is a dangerous combination for me: perfectionist + data nerd + analytical mind set + productivity nerd. It's easy to get carried away and measure and chart things because it's interesting rather than because it is useful.
I have to actively remind myself periodically to focus only on those measures which help me reach a goal. And then, I also have to remind myself to focus on those measures which are leading indicators (reducing carbs and sweets, exercising regularly) rather than lagging indicators (e.g. weight). There's nothing wrong with having fun with QS, but I want to prioritize getting some actual benefit!
If you know people who really get into personal productivity systems (like GTD) there is a similar dynamic at work, and a similar danger. You can spend so much effort optimizing your system, that you have less time to actually do productive work. Investing time in things like GTD have a great return on investment, up to a point. Knowing where that point is, and respecting it, can be tricky if your passion verges on obsession.