Thank goodness for search engines:
en.wikipedia.org/.../Noise,_Vibration,_and_Harshness
I haven't used Dynamat[-like materials], but from the installation videos, it looks like the progression from a little to maxed out goes like this: Picture each panel as a drumhead, start with a patch in the middle where it vibrates most. Then cover it completely. Then add a second layer.
I agree with pursuing wind noise. My Superbeetle has good weatherstripping, but the new weekly driver, the Dasher, doesn't.
My back seat is folded down, I think the reverberation is increased.
In addition to the firewall and floor, inside the doors and in the roof (under the headliner?) are good areas to cover.