i'm not one of the people who drives a beautiful 2014 car with a cd player and aux cord for an ipod plug-in, and in fact, mine is a classic '98 that proudly flaunts cruise control and a tape deck as its fine features. i've had my car since 11th grade (i just graduated college), so the longevity of our car-and-driver relationship has created a certain comfort level. and by comfort level, i mean i don't feel the need to keep it sparklingly clean. or even close to that.
you never know when you'll need a baseball, textbook, spoon, a church bulletin from 2010 or chord progression to an old hymn. you'll be as prepared as this guy for anything. (but actually, anytime i need a pen i can scrounge up like 5 options.) you can also always find something to spit your gum into.
you become a superb saver of money, as you don't waste any bills on car-washes nor quarters at the gas station's car-vac.
you don't have a ton of room for seating because the back seat is covered in schtuff. wait, maybe that's a bad thing.....
you don't have to worry about anyone making crumbs when they eat one of those nature valley bars that must have been created for the sole purpose of creating a mess because you'll be right there to vacuum it up. in about 5 years.
the last reason to drive a messy car is that no one will ever be jealous of your sweet ride. and you wouldn't want to promote coveting, would you?! i didn't think so.