There are surely no hard and fast rules as to assessing the importance of a generalization of a concept. I once took a [look][1] (chap. 9) at debates surrounding the move from groups to groupoids. One important step up for a concept is being deemed essential rather than merely useful. To achieve this it must find its place in an array of good storylines.


  [1]: http://books.google.co.uk/books?id=s37rhfWs73QC