I think the reason why the Wrights, Chanute, Herring, Avery, etc. prefered
spruce, aside from obvious factors, was that it was very impact resistant. In
the pioneer era, it was considered normal to smack wingtips, chaw turf,
noseplant, WHACK, and otherwise "crash" on a routine basis. For example, the
landing gear on my 1902 glider consists of twin 6" high x 1" wide skids...
that's it. Ya wanna land? You're gonna smack the sand with some part of the
plane.

Later, my best guess is that the availability of good spruce, and its cost
relative to aluminum, made it the defacto standard until aircraft speed, size,
and power dictated switching to all-aluminum. Of course, in small aircraft
if you don't have a reason to change, why change? Now that most of the good
spruce is gone, we have a reason to start looking again. Either that, or a
good excuse to drive to Highland. (No Grandma, I really came here to see you!
Oh that lumber on top of my car... oh, that's um.. uh...that's uh... I'm
building a pipe organ... yeah, that's it... a pipe organ)

Harry