The thing about vibration dampening is you do NOT need to cover the entire surface, but rather the parts that will move when the speaker moves. There have been amazing advances in deadening materials but most people still think of just dynamat without taking any of the other types of noise into account.
To dampen vibration, you want a nice thick piece of butyl, and not rubberized butyl, the pure stuff with an aluminum sheet holding it in place; this is what dynamat is, but there are much better quality and/or less expensive brands (dynamat is the single most over priced product out there). You then want to put a layer of closed cell foam (ccf) followed by a layer of mass loaded vinyl (mlv) to totally capture any stray noise. Layering the inside door skin with a vibration reducing material (such as dynamat or any other product that's not as overrated) and at least a layer of mlv will drastically cut down on the noise inside the door panel. I would still dampen the large flat sections of the plastic inner door skin to prevent movement as well as lay some butyl rope around the points of the plastic door skin that touch the door frame to reduce any noise from those locations.
If you want to focus the speaker sound direction, you need to dampen behind the speaker itself, so a ccf cone held in place with butyl rope will greatly reduce the reflected noise from the speaker, and I agree with Mike that you should also dampen the area around the speaker as that's the most common source of vibration if it's not attenuated properly.
My recommendation for a better product than Dynamat at a comparable price is AlphaDamp's CLD tiles, they're the thickest butyl dampener you'll find. I used dynamat on my door skins and floor (I got it a dealer cost, so it was dirt cheap) but I made sure to use the CLD tiles on my roof, back wall, and tranny tunnel. I then covered the floor and vertical surfaces with the Luxury Liner Pro before putting my carpet back in. I can have my stereo cranked to max and you wouldn't hear it outside of the vehicle and even with the windows down the bass doesn't carry. This is where you can check out the AlphaDamp: http://www.secondskinaudio.com/products/AlphaDamp.php