"!Curved tracks even with a spi? What would the advantage be unless the boats dont build much apparant wind when going downhill?"

Thats the point , these highly developed cats (!) carry a symmetrical spinnaker with spinnaker pole mounted on mast and gybed !, they can run dead downwind , not a lot of apparent wind sailing going on there .(admittedly class rules probably preclude an assymetric )

But as Jalani points out they did come up with stuff long before others , most noteably the spin chute which they had for decades , which has now been accepted by cat sailing and changed the whole game for the better , suppose flying a symetrical spin from one didn't look too cool .