I'm going to throw out a bit of disagreement into the thread. IMHO, audio quality matters and there is a noticable difference between low-end speakers and higher end, at least for 90's era onward. For older 80's era games and earlier, probably not so much.
Right now I have a cheap 2.1 Logitech setup on my test rig. The main satellite speakers are underpowered, so the sub picks up some of the mid-range, as well as bass duties. But the sub itself is muddy and doesn't sound so great. In contrast, my main PC uses Klipsch Promedia's (imho, the best computer speakers you can get). Bass is extremely tight, no mud, and the mid-range is where it belongs: coming from the satellite speakers. Even playing something like Street Fighter II, I notice a difference.
So just IMHO, but if you're mainly playing 90's era games and later, it's worth putting a little money into a half-decent audio setup. You don't have to go completely over-the-top, but the difference between the bottem of the barrel and something in the mid-price range is noticable.