Hi Frank, MoI won't let you turn on points if you have an object made up of joined surfaces where each surface has a different control point structure. This can happen easily when surfaces are intersected such as in the boolean commands.
The points are not shown in that situation because it would be too easy to drag the points for one surface and cause a gap to happen along what should be a shared edge, that would tend to put a hole inside what should be a solid skin.
You can view the points by using Edit / Separate to break your joined object into just individual separate surfaces. You can always show points for an individual surface because it does not have this "pull apart shared edge" issue.
Here are some pictures that I hope will help explain it.
Here is a plane and a cylinder that I have booleaned together:
Here are the control points for the cylinder:
Note how there are no control points along the intersection edge with the plane - that edge is what is called a "trim curve", it is a curve that has been calculated that exists on the surface, but is not directly connected to the control point structure of the surface. So you can't modify the surface by pulling on the trim curve itself, the trim curve has its own control points that are separate from the surface's control points.
Here are the points for the plane, just 4 points at the corners:
So you can see here that the 4 points for the plane do not match up in any way to the control points for the cylinder. Here is what happens now if I grab one of the points of the plane and drag it, it opens up a gap:
This is kind of a fundamental thing for how NURBS modeling works, it has to do with the creation of those "Trim curves" that live on a surface but are separate from the surface's control points.
Once you have things set up connected by trim curves, you can't easily modify things by moving surface control points and still have the connections between the trim curves stay intact.
So the whole trim curve system does not lend itself to point squishing, however it is also the key thing that makes boolean operations work well with NURBS models (as opposed to polygon models), since as you do multiple boolean operations the surfaces themselves don't change, just new trim curves are calculated. With a polygon modeler, each boolean operation actually dices the polygon surfaces themselves up into a whole lot of small pieces.
Hope this helps explain it some!
- Michael