It is my understanding that if you put any cast iron pan in a hot (500 degree?) oven long enough, it will slough off whatever build up it has back down to base iron. I've heard of people reconditioning yard sale pans like this.
That technique should work on your regular cast iron without the need for Oven Off, however I don't know what affect it would have on enamel coating. I believe most Le Creuset is rated up to 450 degrees, so you could give that a try.