In a reply to this idea, @xiaoyu-shen said

content helpfulness can be done without logging in

And Content Helpfulness votes don’t appear in user data exports or user activities that come through via the Salesforce integration. (Vote for this idea if you’d like to see that added)

All this seems to indicate that tracking content helpfulness by user would be a prerequisite to both those ideas. 

Long term, I’d love to be able to analyze content helpfulness by user roles, whether using the data export or with improvements to dashboards and analytics.