If it were truly authentic, they would have built it to scale, not simply made it hollow with forced perspective to make us think we're walking through it when we're really not, so obviously, you kinda have to suspend belief (multiple times, I might add) to really get the full effect. You also have to remember that the whole of the park is aimed largely for kids and young teens because, let's face it, that's the demographic that the books aim for. Naturally, there's going to be fans of all ages, but the target demographic will be too engrossed in the rest of the theme of the land to really care if they can see the show building or not. Not to mention, Vyrus' excellent argument.
I'd be more worried about the potential cutbacks to FJ, but from what I can see it's been talked about to death in only a handful of pages, so let's just hope that the cutbacks won't be easily noticed compared to the rest of the ride.