More stuff on spars:
This guy talks about some tropical wood that's stronger. Even sugar maple is a lot stronger, though also heavier. However, compared to spruce you could probaby use half as much and still have a stronger spar that might even weigh less. This is because, since it's stronger, you can use a thinner cap and have more of it near the top (or the bottom) of the spar. The closer the material is to the top or bottom, the more it contributes to the strength and stiffness.
This one's about adding carbon to spars. I tend to think that the amount recommended may be overkill unless you wrap the spar with carbon and perhaps leave out the wood caps and use end grain shear webs that go from one carbon cap to the other. But certainly adding the carbon will make the wing stronger if you do it well. Whatever adhesive you use, test some samples to make sure it won't let the carbon peel off easily.