you can select all the control points on a curve by pressing shift R. now this is a bit complicated but nurbs are considered in the UV direction rather than the XYZ. (even though it is edited in the XYZ space) the first time you click shift R you will add the row in the V direction to the last selected control point, if you then press Shift R again it will switch to the row in the U direction according to the selected vertex (control point). You can also just add to your selection by pressing control numpad + or reduce it by numpad -.
you cant have a row with more points in it then the row beside it ( along the same axis) so if you subdivide it has to be the whole row. a little bit like adding a loopcut to a mesh.