Many people like to measure all sorts of things on (sometimes ad-hoc) scales. "She is a 10" when talking about attractiveness or "He dove a 9.5" for high diving at Olympia. There are many occasions where one would like to introduce a scale and a number.
But you do allow {ni} both with and without a {ce'u}, don't you? I find that odd. Why allow it for {ni} and not for {ka}? I think {ce'u}-less {ka} died out for a good reason, and so in my opinion there should only be one {ni}, either with or without {ce'u}. I prefer it without.