just upgrading your speakers wont do much (depending on what year your honda accord is. if its an older car, new speakers would make quite a big difference). no matter what deck you have all deck have about the same amount of power (between 13 and 18 watts rms per channel wether there stock or aftermarket, dont get fooled when a deck says somthing like 52 watts x 4 this is the peek rating and its not accurate). again depending on how old the car is, upgrading the deck if its an older car will make a big difference. the thing that will make the biggest difference in loudness and sound quality is a 4 channel amp. instead of powering your speakers with your deck you power them with a seprate amp. a standard 4 channel amp will put out 50 watts rms per channal, a huge difference compared to even the most expencive deck. pretty much any aftermarket speakers will be able to handle 50 watts each. but this could go out of your bugit and get very confusing. but it deffenetly is worth it and alot of people make the mistake of thinking that buying the most expencive speakers and a nice deck will give them the best sound quality. if you had the cheapest 4 channal amp you could get say $100, two sets of the cheapest speakers say $40 x 2, an amp wiring kit about $30 and hooked it up to your stock radio it would easly sound noticeably louder and clearer than if you bought say $300 worth of speakers and say a $300 deck. for the bass, just upgrading to new speakers will not improve the bass at all. if the speakers were amplified then you'd get a bit better bass but not much. if you want bass then you might want to think about adding a subwoofer and that will require another amp.
check out this video
http://www.youtube.com/watch?v=Sf3LJYMrdSo&feature=related
