We do mandatory on-call in our unit between October-April. This is mainly to cover the RSV surge that hits the rest of the hospital. Every nurse no matter how much they work is required to sign up for 1/month during this period. Honestly, most of the time we don't have to work. But it is still a pain like you mentioned to know that you might possibly have to work that night. Yes, you get all the on-call pay and call-in pay. I think it is a pretty common practice and something nurses just have to expect.
Just a side note - I laughed when I read your comment about the 3 patient assignment since in our unit we never have more than 2 patients.