I think they could do a hybrid of the two. The original concept art would be a masterpiece if they could finally realize it (while also adding some good queue space). It won't happen with an overlay of the current facade, but it's nice to think about anyways. The castle definitely has some potential, though, with only a small amount of physical modifications.
They should definitely try to recapture some of the essence of this concept by incorporating the posters and signage back in. I'm fully prepared to walk up next year to see the dirty same old castle still visibly standing there with a new sign replacing the Boo Blasters sign, but I think the Sally Dark Rides crew will work their magic on more than just the ride itself.