Once the glass is applied the blades become a cored fiberglass structure.  Strip-plank canoes are a very common example of the structure.  

If one wants to get really techinical the proper way would be to cut the ply in 45 degree diagional strips and laminate where the end grains shown were on the face and back of the blade.  The blade would then be given layers of 'S-Glass' or maybe carbon fiber.

Contrary to the thought of blades needing to be 'thin' to go fast, the tips are flying at close to 100 mph.  Those speeds are considered very low in aircraft and aerodynamic terms.  As the wind speed goes up there is more than enough power to overcome the small drag increase of a 'fat' airfoil. If one care to challange this thought they should look at some data first and show me where to find it.  

IntegEner's post reminded me of some aerodynamic principles that were laid to rest when Monoplanes took over the airplane industry. I will probably do some drawings and models of these thoughts - and may even test them before I claim the hole-y grail of blade design.