Not totally true.
While the material will attenuate frequencies, additive support/reinforcement also occurs for the same reason...the complex phase relationships of the waves passing through the material.
Show me where you plug the wood into an energy source and I'd be tempted to agree with you.
Wood is an ablative and can never add to any regeneration of frequency or vibration except to release it's stored energy in the form of a nice fire.
Complex or even simple wave propagation requires energy input for some less than ethereal source than good intentions and wishful thinking.
"Passing through" any medium always results in degradation since setting the molecules into motion does NOT come free.
Energy IN = Energy OUT minus Resistance. We don't even have to factor-in entropy yet - but I can go there if you want.
Are you thus proffering perpetual motion in a bass guitar? That's what you are saying.
That's the only way to explain additive magnitudes as you've stated.
Interesting concept - wrong, but interesting.
Wood is an energy sucker and has NO ability to increase the amplitude of anything to which it might resonate by ANY magnitude you might want to suggest.
Different woods may suck up different frequencies or tones as they vary in density and all the other factors I've already mentioned.
Variables as might occur in Balsa compared to Lignum Vitae will appear to resonate or act differently - so that's a given.
If you think that's somehow incorrect - just start beating on your house to find it's resonant frequency and then keep it resonating by continuing to beat on it for a while.
'Taint easy. You'll also work up a really big sweat. The energy you put into beating on the house came from the Wheaties you ate this morning. The house will never sweat since it's not working.