In terms of the magnetic flux, no. Increasing the rotor thickness actually decreases the reluctance of the flux path in the rotor. But there are other issues that are not affected by the rotor thickness. See my other comment on rotor saturation of this day for one that is usually ignored. A thicker rotor will also act more like a flywheel, which could affect the dynamics of the wind turbine. One could lighten the weight by a judicious placement of holes, however.