My car stereo has this bizarre need to increase the boomey frequencies, which is really annoying. And, when I try to mix it out, then the tracks lack low end on other systems... If taking the door panel off to replace the speakers wasn't such a PITA, I'd swap em out. But, it does give me a sense of what other people's crappy car stereos sound like.
And by boomey, I don't mean the 100-200k huge low end, but more the 2-400 range with some odd spike in there of that one range I tend to remove from guitar and bass tones.