Ummm, I'm a forestry school graduate and have thirty-years of guitar playing, but I got no comment on that spruce comparison yet--insufficient info. Can you mention a few instruments built with one or the other?

As for Rosewood, I'm pretty sure Brazilian is heavier and more reflective of sound. I have an old Giannini dreadnought--a cheap made in Brazil guitar. It's got solid BRW sides, I think and a lovely BRW veneer back. The top is ply, badly mangled where I removed the bridge a few years ago. I'd love to recycle this guitar into something with a new top & bridge. It had a terrific clear treble sound.

Bill