I haven't studied your post in all details but the theme enclosed in them is correct. In the end, as I think you say, the spi creates one overall force that can be devided up into 3 components. In summary these are :

-1- a horizontal force along the centreline (drive)
-2- a horizontal force perpendicular to the centreline (pushes the boat to lee)
-3- a vertical force

These three forces create in turn 3 moments around the CE of the hull and daggerboards becuase the CE of the spi sail isn't at the same place as the CE of the hulls and daggerboard.

Force 1 and 3 result respectively in a counterclock wise moment (when looking at the boat from port) and a clockwise moment. Wether the bows are lifted or pressed down in absolute sense dependent on which one of these two moments is larger than the other. On beach catamarans the moment linked to force -1- is bigger than the moment linked to force -3- and so spi doesn't lift the bows in an absolute sense although the vertical force does lift the whole boat out of the water a little bit. To makes things simpy right !

If this is what you were getting at then yes I think you are correct.

However as we discussed elsewhere this is only part of the story that explains what sort of effect adding a spi has to a catamaran

Wouter