IMHO, car noise pollution tends to exist in the lower frequency range. I am able to clearly hear high frequencies at both 0mph and 80mph+.

I think this effect emphasizes high freq and makes mp3 distortion sound _worse_! Mp3's have the hardest time with high frequencies - they are trying to encode high bandwidth information with relatively low bitrates. Although in-car noise pollution may mask lower frequencies, I can travel 100mph and still cringe at the flanging and other distortion present in a bad mp3.

While the car is a very bad listening environment, I have been very happy improving the audio quality of my system, as well as encoding mp3's at higher bitrates (320kbps). I've even gone as far as running S/PDIF digital to the trunk, where I have a studio-quality DAC modified to run off 12 volts.

Home-audiophile quality? No. I do agree there is no point in spending thousands on a car system. However, with my schedule (and my commute), I really only get to listen to music in the car. The hundreds I spent on DAC/amp/speakers were worth every penny!