I can't tell that it made a significant difference. I did it since I had some spare material. It certainly reduced an engine noise heard outside, but most in-cabin engine noise comes through the firewall. I tried to apply some dynamat to the firewall. It helped, but after several months and HOT summer, the black tar started melting and the whole piece is sliding down - so far about 1 inch and stabilized. I think that the right solution is a fireproff firewall. I'm thinking about getting a VW piece from Whitney catalog, cut it and attach. Spring project.
I would suggest putting dynamat under the carpet - inside. On driver and passenger side too.
I can say for sure that the biggest noise reduction came from fillig "resonace" chambers behind fenders. Well my 18" Pilots are noisy.

 

So far I have the Fenders dynomatted and I sprayed some underbody coating to it. I also put some insulation in the chamber area wrapped in a plastic trash bag, and it seemed to help a little.

When you dynomatted the floor, did that help out more compared to the stuff you did to sound deaden around the wheel well?