Re: dip plastic vinyl spray (e.g. plasti dip, sprayplast)
IMO...
Thin, hard coatings, such as automotive paints and clears, or thin coats of nitro, don't have a huge effect on tone because of their hardness. Vibrations travel through them without much dampening effect.
Plasti dip is both thick, and soft. It will absorb the resonances from the wood and dampen them, and will have a greater effect on tone. Kind of like singing through a pillow.
Not saying that the tone will be better or worse, but I would expect it to be different.