Sail Twist

In general you want an untwisted leach so that the air flows across the sail in a uniform way at all heights up the mast. In light winds some twist can be good, as the wind gradient means that the angle of the wind is different at different heights (due to friction with the rotating earth). Therefore twisting the sail to suit the wind direction maintains the uniform flow. You are right, twisting the sail in strong winds is one way of spilling excess power, but it is not generally the best way.  It is usually faster to flatten the sail as much as possible (lots of kicker, downhaul and outhaul), lift the daggerboard, hike like hell and ease the sails if needed.

In my experience it is better to have a flat, flogging sail than a full twisted sail (it is not really possible to have a flat twisted sail, 'cos the kicker must be eased to get twist, but easing the kicker straightens the mast and therefore powers up the sail). 

I've not sailed a Vago, but you have an untapered (and therefore stiff) mast I think.  This probably makes it hard to get enough mast bend to flatten the sail fully by pulling on the controls.