Here we go:
1. A snapperhead will make my tone better - False.
2. It's an integral part of the 'Nashville' sound - False.
3. It will add sustain - True.
Any player worth their salt will most certainly tell you that good tone is in the fingers. Snapperheads are best for beginners. Most players who've acquired some experience have pretty good muscle control in their fingers, which renders a snapperhead virtually useless. There's nothing wrong with jamming one, just digest the right information before you plunk down 150 dollars for a unit if you really don't need it (i.e., a cat who plays with one on all the time). If you want to use it as a lead boost in front of your od, do it. They can work pretty good for that.
Let the flames begin!