There is a limit to how thin you can go and still retain stiffness. Hull stiffness relates partly to the distance of the separations between the two glass skins. The core thickness is as important as the core density in this respect. I like the look of some of the heavier timbers, but I keep them to pinstripes and accents so the weight doesn't add up too much. I rip my strips to 5mm. It is a thickness I feel is an optimum balance between weight and stiffness for a kayak.

If you sit on the rear deck while sliding into an ocean cockpit, for instance, you don't want it flexing.

Nick has been using thin mahogany recently, but that is a relatively strong timber.

A lot depends on how much punishment the SUP is going to have to take. standing on a flat surface is putting your full weight on a very small surface. I would think that if you were going to reduce thickness anywhere, the hull would be the place to do it rather than the deck.

My thoughts.

Et