When you are trying to add new points to a mesh, check that you have the polygon method selected (rather than the rectangular or rotated rectangular method); this should bring up the new mesh points dialog box.
actually, having just checked in AC13, this is how it works for adding individual points; using the magic wand, it doesn't seem to matter which geometry method is selected - just ensure the target mesh is selected and that you have the mesh tool selected when you apply the magic wand to the spline/contour.
you don't mention which version of AC you are using; it's a good idea to add your software and hardware specs to your signature (in your profile) as sometimes things change between releases.