One of my previous good-sized shops had a preps-only columnist, and he was not essential. You tend to be a little softer around the high schools, so the columns read more like coronations and features than debatable opinions. A real luxury.
He's soft because he wants to bee soft. You can be hard and cover the preps effectively. I know it's high school and kids aren't compensated for their play, but there are a ton of stories out there aching to be told.
I think it's a great idea for any paper, especially if there is at least a major university in the area. The question of who on a staff should be doing it is the tough one. I think in a perfect world, the ME, publisher and SE should look at the personnel and go with someone who has good writing/reporting skills and is not afraid to take a stand on issues relating to the local teams. I've read way too many rah-rah guys or columnists who write stuff on pro teams three or four hours away. But the reaction to a good, thought-provoking column can be stunning.