Dustmaker,

I would not use plywood to replace the wire struts as I would hate to have the upper wing part company with the fuselage. A possible alterative would be carbon fiber tube or rod, much lighter and stronger than the plywood. As most Smiths need some nose weight, do what Dave suggested and lose tail weight. The wire struts are forward of the CG for the most part and the weight saved forward of the CG may need to be replaced with dead weight. I think a step up in motor/battery size may be a better choice and use the batteries to help balance.