Nicholdime,
Are you sure that no other aerodynamic improvements were made to the old glider that you recovered.
If not, then you have provided the response to your question.
If so, then the form drag may be more influential than the skin drag (as I suspect).
http://en.wikipedia.org/wiki/Parasitic_drag
http://www.grc.nasa.gov/WWW/K-12/airplane/shaped.html
http://en.wikipedia.org/wiki/Friction_coefficient
Of course, the final performance results by improving the friction coefficient of the skin depend on several factors (amount of wet surface, coefficient and condition of old skin, velocity of flight, etc.) and it should be different for each case.
You can determine the difference in friction coefficient of each skin by testing a sample.
The material should be used as the surface of an inclined plane.
The coefficient (between the materials of the skin and testing block) is always the tangent of the angle at which the block starts moving down the plane.
http://www.ejsong.com/mdme/memmods/M.../Friction.html