As nice as the Sanctuary might be, and areas similar on other ships and cruise lines, I don't think you should have to pay for that. It just gives cruise lines more of a reason not to enforce it. "Well, if you can't find a seat here go pay for one."
When we were on the Grandeur in February there was someone in the show lounge saving a whole row of seats for thirteen people. Even though up on the side screens a ticker was saying "no saving seats".