I've been working on a project along these lines recently. I've called it Dogsheep - the basic idea is to have scripts that export all manner of my personal data (from Google, Apple HealthKit, Twitter, LinkedIn etc) into SQLite database files, then use my Datasette web app to browse them and run interesting queries.
Whoa, this is super exciting to me. I've been looking for something that would get some of these types of data into a web-based interface that I could package for Sandstorm. This looks like it would potentially work for that fairly easily.
I went similar route after discovering Google Checkout refuses to return my YT comments. I wrote quick&dirty tempermonkey script logging submitted HTML forms (addEventListener "submit").
More about that here: https://dogsheep.github.io/
The tools I've built so far are under https://github.com/dogsheep