The frequency I used, 329.63Hz, is the high e string frequency. I used this because the formula I derived only accounts for open strings. The thing I overlooked is that harmonics also vibrate along the full length of the string, and can be used, and these harmonics are the overtones you hear when you pluck an open string.
Octave harmonics are the most audible, and occur at frequencies that are powers of 2 * the open string frequency. This corresponds to a length that is one over that power of two. So, the first octave harmonic occurs at 1/2 the string length, and is twice the frequency of the open string.
On the maple/mahogany laminated neck mentioned above, an amplitude reduction of 10% occurs at a frequency of 4185Hz (scale length of 25.5"). This is around 16 * the frequency of the open B string. 16 = 2^4, so this is four octaves above the open B string. Not all harmonics occur as natural overtones, but it's safe to assume that an octave harmonic would occur as an overtone.
As you increase the distance between the fundamental pitch of the string and an overtone, the amplitude decreases. 16 * the fundamental frequency is going to be MUCH quieter, so this reduction, although significant, may not be audible because this overtone is so far from the fundamental frequency.
I'm going to do some more in-depth work on this problem, since you end up with some interesting interference between waves originating at the nut and the bridge. That, and resonance could have some interesting effects.
One thing I'm particularly interested in investigating:
Waves moving in opposite directions interfere and form standing waves, not unlike the vibration of a string. There are particular positions along the wave that will always be the peak amplitude, and others that will always have zero amplitude. I'd be interested to know if placing a pickup at a zero amplitude spot would sound different from a pickup at a higher amplitude location. Keep in mind this amplitude is for the body's vibration, not the string.
-------------------------------
As far as speed of propagation for sound through wood, there are many factors that could affect this speed.
1. Each piece of wood is unique. There are no concrete rules, since imperfections (including desirable ones, like figuring) can affect transmission speed, as well as natural variations in density/water content.
2. Sound propagates at a different speed for each frequency, as well. In a medium like air, the variation is so small for the audible range, we stick with a single value. In wood, the speed is significantly higher (by more than a factor of 10). The variation due to frequency may actually be worth looking into. I'll get some concrete numbers for this.
3. Tension on the wood will, with absolute certainty, affect the speed of propagation. Speed along the grain is much faster than across it, so the fastest propagating sound waves may follow the curved path of the wood grain if the neck is bent. When you're talking about small percentages in interference, this difference can be significant.
4. The width of a piece of wood will affect its resonance. At some frequencies, propagation along the width of the wood can lead to interference in the length propagation, effectively reducing the transmission speed.
5. Environmental factors like temperature, humidity, air pressure, etc... will play a role in sound transmission and resonance, so these may be worth looking at as well.
So, in the end, the problem becomes MUCH more complicated. Developing a good model will be difficult. Luckily, the wavelength of your low E string is around 10 meters when traveling through maple. This leaves a lot of room for error. My intuition tells me that laminated necks aren't going to have any real effect on the sound of the guitar. More important will be the relationships between bulk masses in the guitar, and their resonant frequencies. The contact area of the neck joint could really affect the resonance of the instrument as a whole. I'll have to brush up on some acoustics and look into this to give you a real answer though.
----------------------
This could be only due to the mass change. The relative volume is the same, but mass is greater, so density is higher. Water is also a terrible conductor of sound, so the sound waves may take jagged paths through the wood. Since the simplest look at resonance depends on the length of the longest and shortest possible "paths" for the sound, the change in humidity could easily change the character of the wood. You're not just imagining the tone difference either. Again, the water is probably the culprit. A slow sound transmittor decreases wavelengths, lowering the minimum frequency for interference. You'll lose more overtones as you introduce more water into the wood.