BUT, I might have the opportunity to get a 5 m2 kite not used or almost not used, and one I know is good at a good price suddenly.
So have had three 5 m2 kites quite often, slightly different characteristics.
They dont hold up, as used a lot when riding waves, and might be thrashed so they get punctures - THEN it is perfect to have a spare
My strategy is different though, instead of having a spare kite, I have small increments in sizing
This way I actually have a spare kite if something goes wrong - can just pick one 1 m2 bigger or smaller, and ride on.
It also makes choosing a kite a lot easier - when you have small increments, you can pick exactly the size you think you need (might not be correct, but that doesnt matter), so a lot better.