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They fly better without a kilo of sand stuck to them.

Check with the manufacturer but I don’t think I’ve seen a recommendation other than dry and no sand. Also some reported problems using compression bags.

Bars - I’ve seen recommended fresh water soak or rinse.

Harnesses and boards - never seen a recommendation.

Then there is rolling or folding...

I think I picked up something sharp once that made a small cut while the kite was in the bag.

never did

I think salt water when dried out acts like salting meat, to preserve against bacterial or other organic life degrading the kite.
On the other hand... every salt crystal that crystallises between the fibres introduces a weakness under tension.
Fresh water is probably better for kites but even the act of folding and unfolding a kite will gradually wear it out.
If you hang out a kite to dry, hope that no birds, cats, insects or other wildlife damage it. I've heard of ants invading and eating kite bladders.
Degradation of the fabric from the sun's UV is a more serious issue I think, especially here in New Zealand where melanoma incidences are particularly high.
Also loosing weight ...I need to! to reduce the stresses on your kite!

I only rinse the bridle pulleys to get any salt and sand out so they run smoothly.