Don't knock Plywood
it's an immensely strong structural material with a micture of natural wood fibres and modern polymeric resins. It works very well.
I'll bet that the failure of the X-Wing was to do with the joints (especially the ones they wanted to MOVE * ), and not with the sheet/body materials...
* The F111 swing-wing fighter had IMMENSE problems with a moving-wing geometry, and they had access to aerospace composites and almost unlimited budgets.
I think you'll find that the first flight test model of MOST swing wings fell apart...