I would think that aerodynamic drag can have an influence on the support arms that the balls are attached to. Round carbon fiber rods are relatively stiff, very light weight, and are available for R/C foamy models. A symmetrical airfoil shape would exhibit less aerodynamic drag. K&S sells light weight airfoil shaped aluminum tubing that may work also. These won't be as stiff as Eric wants, but may still have some advantages to long term motion, especially in larger examples of this device.
CarveOne