Does the leading edge come to a sharp edge or does it have a radius? If the leading edge has a radius, and the trailing edge comes to a sharp edge, then there are not two sides. To make two sides you will have to split the leading edge radius at some tangent point, which seems to vary through 3D space.
Extracting a surface halfway between two surfaces is not simple. In SpaceClaim, it would be fairly difficult. A surface modelling tool like Rhino is more likely to have tools to find that center surface.
Say you get the center surface, and you mesh the surface with shell elements, how are you going to assign the thickness to each element? I have used NX CAD/CAE software that can generate a midsurface between two nonuniform surfaces, and mesh that midsurface using nodal thickness, so each corner of each quad element has its own thickness. I don't know how to do that in ANSYS.
If you only have ANSYS, I suggest you use solid elements to capture the stiffness of the wing.