Here's my experience:
I'm a high school student, and my dad lives on the campus of my boarding school. This lumps me under "residential faculty", "day-boarder", or "lucky", depending on whom you ask. However, one of the main benefits of this is that I'm effectively an unpaid night-watchman. Daytime restrictions don't really apply to me. I've learned the nuances of working with each of the school's night-watch people, depending on whether I'm up for their dry humor.
Wandering around campus with the night people has always been interesting. I had to learn the differences in each. One of them got slammed in the ear and can't hear. The other two have ears like a bat, but one of them has troubles in one eye. On a logistical basis, listen and spot are very much separate skills. On the same note, however, I don't think they're skills at all.... but neither here nor now.
I could very much see this being useful for one class-- Give it to rangers. Effectively, it becomes a mega-class skill. Even if the ranger is deaf, he's gotten so good that he can sense the vibrations. Blind? He has an enhanced sense of smell, or something similar, and he doesn't need sight. You, as a badass ranger (who just gave half his salary orphans... orphans with diseases), have trained yourself to overcome your limitations and only have to spend half the points. However, for the going-blind elven mage.... they are very much separate skills, and it will throw him off.