Only time would really tell, but I'd figure that LOTR would not be as big a draw.
I am a big LOTR fan, but I don't think it translates to a park in the way that Harry Potter does today or that Star Wars does.
When I was a kid and saw the original Star Wars movie, they dominated my imagination & play. I'd pretend to be a Jedi, play with the action figures & ships, or even just daydream about what it would be like to be in a Star Wars world. As I got older and Lego finally released their Star Wars line, I bought every one that I could. When the Phantom Menace was going to come out - wow, I remember the excitement that everyone had (unfortunately, it didn't turn out as good as everyone hoped)
Potter had some of that - the imagination of being a wizard, the wonder of Hogwarts, etc... It even had the Lego sets
Amongst the two, I think (at least for me), Star Wars captured my imagination in a way that Harry Potter only scratched the surface of.
When I look at my kids, they love to dress up as star wars characters wear their "Hogwarts" robes. They can imagine what it's like to live in those worlds.
LOTR, on the other hand, is a great set of books and some tremendous movies - however, I don't see how you translate that into theme park wow & excitement. My 8 year old can't see himself in the LOTR, he doesn't dress up as a hobbit. Even as a kid, the only character I marveled at was Gandalf. Basically, as I see it, LOTR is a GREAT!!! story, but when it's over its over. Star Wars is the king of keeping my imagination. Harry Potter a distant second.