I found myself searching through server logs to find when anyone last accessed a particular extension in /administrator when a friend of mine called and asked if it were possible to log changes to extension params.... Sometimes you can't see the forest for the trees! I immediately set out to create such an extension. Now there is no confusion as to when a change was made, or who made it. By the way, I found the log I was looking for - and it was me who made the change!
With this plugin, each installer event on your system is logged. New extension installs, manual updates, automatic updates, uninstalls and even extension param changes are logged.
The plugin has a log viewer, allowing sorting, drill-down, and filtering by name or user.