I always thought nose hairs were a hold over from ancestors for which having a filtration system for air coming into the body was important and made them more likely to survive. It kind of makes sense in that engineers include air filtration for lots of different things...auto intakes, cabin filters, AC and heating systems.
But it would actually be a better question of IDers. Evolution often leaves animals with odd and unruly adaptations that are either hold overs from ancestors and/or barely adequate for what they ostensibly do. That is understandable. But why would an intelligent designer intentionally create beings with...difficult to manage, inefficient and poorly designed features. IOW, these little design flaws suggest evolution and not ID...unless the designer is a moron or cruel.