It is also unlikely that clip-on tuners affect the sound much. There is a device called a fatfinger that you clip on the headboard and it supposedly eliminates deadspots in the neck. By changing the mass of the headstock, goes the theory, we change how much energy is transferred into the headstock which then changes how the sound is transfered through the neck and thus eliminates the deadspot. I have never used a fatfinger but those who have say at best it merely changes the location of the deadspot and moves it up or down a fret but most people it had no effect at all. I also only know of them being used for bass, I don't know if they have them for guitars. Regardless, they don't really work and they change the mass of the headstock or neck way more than a clip-on tuner or a capo. That's why I have yet to see a professional musician use or endorse a fatfinger and why I do see professionals use clip-ons and capos without reservation, I'll bet.

To me, I think what really changes the sound of an acoustic is the cutaway design as opposed to the full-bodied guitar. I think that affects the sound a great deal.