The funny thing is that I have been using loads of the tools frequently for over a week now due to my trying to gather info regarding my other Community Support query about Active Cachers.
I have used multiple times (typically anywhere from 5 to 20 times) the General Overview, Top Logged, Top Finders, Top Days, Logs over Date, Top Hidden, Top Karma and a few others.
During all this time my Site Activity Points have remained static.
I was expecting them to be affected by my usage, but they weren't hence my query about what actually constitutes Site Activity.
I'm just one of those annoying people who loves stats, but they are worthless if you don't truly understand them :)