Dead spots on a bass guitar
Indeed it's not easy to improve on an instrument with dead spots.
The relationship between body, headmass, and the structure of the neck determine the tone qualities of an instrument (along with the dead spots). The first cause of dead spots is a weak piece of wood for the neck. Neck structure, type, and location of the truss rod(s) can avoid most of the dead spots but a bad piece of wood always makes a bad instrument.
In a way, it very easy to radically avoid dead spots, but the tone of the low frequencies will suffer! The main problem is to find the exact balance between a real good deep and responsive low end, and the absence of dead spots on the high end. That's the art of luthiery. Dead spots are not always a lack of volume, often it's a lack of the fundamental frequency. When you play the note, the fundamental sounds like it is omitted because it has no sustain, while the first harmonic goes on vibrating normally.
Since the bass guitar has a very long neck this acoustic problem is mulitplied! For that reason, it is a real acoustic instrument, and that's why I love it. A good luthier sculptures the tone of an instrument by choosing the structure and dimensions of the instrument, according to the pieces of wood and the musician' choices. It's a difficult task, it needs a lot of attention to the client, and excellent technical and scientific knowledge.
A lot of my clients ask for no risk of dead spots and in my opinion, it's a mistake. The most captivating instruments I have played often have some little dead spots somewhere. Many good bassists can manage around this problem.