I think there is a new epidemic in America. I call it crawl space phobia. People don't like that dark area under their stairs. It will never be pretty or well lit, but it can be functional. So get over the fear and us it!! Usually its a great storage area.
I would consider it "cold storage", since its a little harder to access. Its great for holiday storage. You should always pack your items in plastic bins to keep them safe. Its also great for memory items. Some of my other clients have used it for left over remodeling material or suitcases.
Whatever your choice maybe, its valuable space that should be used! Don't overcrowd your other areas or closets!