Regarding the date the prices go up - this is what I got from NCL:
You are correct in that Cirque Dreams and Dinner and the Murder Mystery prices are changing on Norwegian Epicís 9/25 sailing because of the high demand and popularity of both. In addition, with Cirque Dreams and Dinner we are enhancing the menu starting on the 9/25 sailing.
I am the editor, but I also speculate, ask questions and play devil's advocate. I reserve the right to change my mind.