I have spent a lot of time with Quantified Self and in that community. From there my impressions:

1) Structured experimentation doesn't come naturally. It's hard work for anybody in that community. At the beginning I would have thought that a lot more people get into it, but it seems to be a really hard habit to pick up. There seem to be strong cognitive barriers that you have to overcome.

2) Getting claims specific enough to be testable is hard.

3) Reflecting about what you learn in writing is useful even if you can't put numbers on things. Having questions that you care about in writing in Evernote is useful.