That's interesting about the spinnaker luff tension. It was the opposite effect when I was sailing dinghies. In the 125's with a symmetrical traditionally set kite, we would drop the pole on tight windy reaches to reduce the overall "power" of the kite. The major effect was that the sheeting angle was lowered considerably which opened up the leech a lot, hence depowering the kite.

It was amazing to see my brother with very light crew (40-45kg) in 20 knots on a shy reach blast away from everyone at a national titles heat because he had dropped the spin pole till the luff was tight. Only the heavy crews could even keep the kite up with theirs set normally, let alone be in full control and keeping up with my brother. Everyone else had to drop their kites and two sail reach to the bottom mark. It was phenomenally quick.