imo sounddeadening is is one of the best bang for the buck upgrade you can do... for around $300 you can do pretty much 70-80% of the car and the difference is night and day. It literally makes a corolla sound like a lexus ls or a civic sound like acura rl... (these are the only comparisons that i can give because i've been in them), barely any road noise, traffics seems extremely distant, hel l if you put on ocean sounds you'll actually believe your in fiji lol. Proper sound deadening will make the midbass pound, the tweeters have more clarity and authority, and of course the sub will wang like crazy... also sound deadening keeps sound in so that's good for both overall sound stage and security, you can blast a bit louder without catching thieves' attention.Im going to do this too. Leonsv, recommended that I pick up "second skin damplifier." He gave me this website to check out, http://www.sounddeadenershowdown.com/ (they tested many, and picked damplifier, high quality/durability and cheap price). He said to go in this order based on how much money you have... front doors -> rear doors-> trunk->floor->rear rack->firewall->roof. If you do your trunk and front doors I think it'll cost you $50-100, not including labor.
Overall I think its worth it, especially since youll probably have your car for a while.