Have you considered a limit on user interactions per day? 10 posts/comments a day and 10 upvotes a day?
It seems counterintuitive to restrict users interacting with your platform, but I could also see it working the other way (I want to login and use my daily allowance instead of losing it).
It seems counterintuitive to restrict users interacting with your platform, but I could also see it working the other way (I want to login and use my daily allowance instead of losing it).