...The conclusion is that every curved board has an equivalent straight board with roughly half the angle and a bit shorter. This reduced length leads to a smaller drag that is negligible in the big picture since it is much smaller than the hull drag.
Vertical lift always comes at the expense of increased dagger board drag. The next question is if it is offset by an even larger reduction in hull drag...
The first part of your conclusion makes sense. From my personal experience, curved boards are used instead of straight boards for practical reasons: they are easier to insert, lower and lift. Otherwise, straight ones are lighter, easier to build and less draggy.
As for the second part, I would look for benefits in terms of added stability and damping, not in terms of drag reduction. The additional stability and damping improve seaworthiness and may save some energy from unnecessary pitching, heeling and yawing motion. Alternatively, it would allows for a more powerful sail plan.
