I would guess Steem activity levels in the US, Canada, Europe (western) and Australia etc have risen as the STEEM price has risen in the past - and the opposite as the STEEM price has fallen.

I completely agree with this assumption. I remember when the price of STEEM was higher, it was immediately noticeable that the amount of daily published content was increasing dramatically, long-abandoned accounts were becoming active, and guests from Hive were appearing.