the paint on sound deadener is pretty good stuff, buts its nowhere near as good as the stick on stuff, becuase it weighs more. Shop around you'll be able to get 12-13 square metres of stinger roadkill for around 90 bucks i think? got it from jb hifi about a year ago, cant remember properly.
if your talking about the plastc stuff convering the inner door, you should leave this as it protects the inside doors skin from mosture.
generally if you do the doors properly it will reduce a fair bit of noise, and also when closing the door, it would sound more solid.
also why you doing this for? aftermarket stereo? or just a general reduction in road noise?