Do it!!!. I did mine a it helped a ton. I have Eclipse speakers in my doors and they would buzz the panels and doing the dynamat fixed it all and then some. Also quieter without radio on too.
I still have Mach 460 equipment and dyno'd the doors. I noticed my door clunks closed now and there is more sound coming from the door speakers. Some road noise is gone, but not much due to my stang being a vert.
It would be good idea to do it but let me warn you: This is something that you will become addicted to. It will help on some of the noise but then it reveals a noiser part of the car. Maybe the noise will be quieter through the doors and then you notice it more in the floor, or in the trunk ect. Also, I wouldn't use dynamat b/c it is inferior to SecondSkin Damplifier (dynamat cost too much for an inferior product). Check out my sound deadening install
This would be a good forum to ask questions and you can also click the link at the top of the forum page and it will take you to secondskinaudio.com. Check out the products.