If you've never been before, it's worth the trip for an evening family activity. They have a brand new visitors center that just opened up that sounds pretty cool.
The pics here are some from a couple years ago when we took our family to see it. The visitor's center had tons of hands-on activities for the kids to experience. We watched a short video on the mine and spent a lot of time watching the ginormous trucks go by. They're easily the biggest trucks I've ever seen!