Exec Tourer with "Premium" sound system: 4 Woofers (one in each door), 2 Tweeters (in top of dash), 1 sub (in boot wall). Best stock sound system I've heard in a car that isn't a top end Jag or whatever. Shakes the car nicely, never distorted it and drive it pretty hard. Now the car's getting older, it's rattling door panels a bit which probably want some firming up, but the system itself is awesome. Have no desire to change it.
I think if you factor in road and general car noise, it's pointless to go too overboard on car sound systems for general use. There will always be noise pollution from the car and road and in fact more attention should be paid to insulation over sound system. With that in mind, I honestly don't think I'd ever want more from a car stereo, and I'm a sound engineer.
But then those who enthusiastically fit amazing stereos in their cars, to show standard. I got time for that, that stuff cool. But it's a different take on car sound systems, more of an enthusiast/hobby approach. Like the sound equivalent old hellaflush lowering. Relatively impractical, but very, very cool. Haha!