Upon further thought I think I know what is going on with the spi.

My assumptions are:

1) All the forces on the boat act about the center of buoyancy.
2) Forces created by the air acting on the sails can be reduced down to a center of effort and a vector eminating from the center of effort

Now, depending on where the center of effort is on a spi and at what direction (vector) the force is acting from that center of effort will determine what torsion is acting about the center of buoyancy (CB). If that center of effort (CE) is below the major horizontal chord of a circle whose center is at the CB and a radius at the CE, then any horizontal component of that force (in 2 dimension looking at the port side of the boat) will produce a clock wise torque, therefore lifting the bows. Also, any vertical component of the force will produce a much larger clockwise torque.

If the CE is above the major chord of the circle described above, then any horizontal component of force will produce a CCW torque about the CB while any vertical component of the force will still produce a CW torque.

In my above explaination the vertical and horizontal components I am referring to are of the force that is perpendicular to the cirlce described above. This force is a component of the spi's overall force vector. I hope this makes sense to you all. In my head it is perfectly clear.

Since I don't know where the CE is on a spi I can't be sure if this is why everyone thinks it creates lift.

Now, as to why a spi "settles" the boat down on a reach. Take the same perspective looking at the port side of the boat. I knwo for a fact that the CE of the spi is out in front of the CB of the boat. This means that the spi is dragging the boat forward versus pushing it. As you know it is easier to pull something in a straight line than it is to push it.

I guess I should have taken that technical writing course as an elective instead of wine tasting. This is much easier in person with a pencil and paper.

Let me know if I need to clarify anything or if I am making absolutly no sence at all.