Though I think they add a more aggressive look to the car, I use the mud flaps for purpose. Like Greg said, the rear 1/4's chip, and I find that the bottom of my rear bumper gets lots of rocks and dirt too. I will be driving my Lancer this winter as well so it just made sense.

Something else I invested in for mine was a set of Weather Tech floor mats. A little expensive but they are a perfect match and they are the best floor mats I've ever seen.