The curvy daggarboards are too hard for my pea-brain to comprehend, so I'll stick with the simple canted-daggar style.

Am I correct in presuming that a canted daggarboard is more effective going downhill than uphill?

Would the vertical (zero cant) orientation be better upwind to counter the leeway? Or would there be some benefit of vertical lift (i.e., lifting the hull out of the water) with the heeled boat going upwind?

If this is true, is there a good "average" degree of cant that works for beachcats with spins (typically heeled about 15-20 degrees already)?

Any foil creates lift and that lift is at right angles (90 degrees) to the direction of flow over the foil. If you have more lift than you need to prevent side slip then you can either pull the board up to reduce drag or use some of the lift to reduce drag by reducing displacement (this is where the canting or foil bending comes into play). This is true regardless of the wind direction. If you spend millions on design and testing (think AC) you can probably know precisely how much lift is being generated in any condition. Beach cat sailors can guess or get a decent idea by sailing a lot with different foils and settings in different conditions (think A Cat development). If you spend a lot of time and money developing this technology and knowledge then you are probably looking for a way to make it pay off for you and that usually eliminates giving either away for free. So you either have to do the work and spend the time, buy the developed products, or be prepared to except the free opinions of the masses. If you choose the last option, be prepared to feel cheated!

FWIW, I have read that the foils that are bent at right angles produce verticle lift most efficiently and that seems to be borne out by the AC 72 boats so far. These are problematic to build, install, and operate so it may not mean much for beach cat owners yet. I hope that this development quickly reaches a point that it can be used at our level on a practical and easily affordable basis but it appears to be not even close to that yet.

I was thinking more of the canting keel concept, except for daggars whereby you could cant zero degrees upwind and move it to 10 degrees or so (inward cant from hull centerline) downwind.

But a curved foil may do that more easily? Instead of moving the cant, you just raise/lower the curved foil?