The fact that it is a sequel to a movie that flopped over two decades ago is a very, very valid argument. Name another hit movie that was a sequel to a 20+ year-old-flop? Off the top of my head, I'm not even sure such a film has ever been made.
The word I've heard from those sneak previews is that the movie is visually stunning, but has a weak story filled with mediocre acting and family melodrama. Strong visuals and a weak story is what sunk the first movie.
While the movie has some buzz, it may be overshadowed at the box office. There are a lot of high profile films competing this holiday season. Harry Potter's going to do crazy business (though it should be mostly played out by the time Tron opens). The next weekend, you've got Tangled. I'm worried for Tangled opening so soon after HP, but if it catches on it could actually steal business from Tron a couple weeks later.
The week before Tron, you've got Narnia. And this one looks a lot better than Prince Caspian. Again, I think Potter hurts Narnia. But if Narnia catches on, it could still be doing buisness when Tron opens.
Tron opens against Yogi Bear. And I am confident it will win the weekend with a big opening. But, I also would have predicted that Princess and the Frog would have cleaned up against Alvin and the Chipmunks 2 last year. Yogi looks to be in the same Alvin mold and could surprise people. If it does, it takes a chunk out of Tron's audience.
(Before anyone jumps on that, I feel safe in predicting Tron will open at #1. I'm just saying it's possible Yogi Bear or a hold-over from a previous week could take a bite out of the opening weekend.)
The second week will be critical for Tron. It's almost guaranteed a big weekend. But if audiences don't love it and it takes a big drop in its second weekend, it will be viewed as a disappointment because expectations are sky high. Little Fockers and Gullivers Travels both open the next weekend and could compete for Tron's family audience. True Grit could pull away some of the male/action audience.
But I think the key will be the quality of Tron. If it's just a pretty sci-fi movie, I don't think that will be enough to do block buster Pirates-level business. It's going to have to deliver a compelling story that appeals to more than gamers and fans of the original cult film. And what I'm hearing is that on that level, the movie falls short.
I like Tron's prospects to be a holiday hit for Disney. I think it will be the franchise they were hoping for with Prince of Persia. They desperately need it to be. But there are plenty of reasons to think Tron will under perform. There's only a few sure things at the box office and Tron Legacy isn't one of them.
While I do agree with you that quality will ultimately tell the tale when it comes to how Tron performs overall, I have to disagree with you on your box office assessment.
Harry Potter and Tangled are pretty much non-issues when it comes to Tron. I'm a big Potter fan, but the movies usually do their damage in the first 4 weeks, leaving pretty good space for Tron. As for Tangled, while I think it may perform really well, I think the audiences for the two just won't have as much overlap, and like Potter most of its business will have already been done by the time Tron opens.
Like you, I think people are underestimating Narnia, but I think it's very likely that if it does catch fire, it will not be to the detriment of Tron, and that the two could a have a bit of a Sherlock Holmes/Avatar relationship.
As for Yogi Bear, even if it is a big success, the audiences just don't really match up that much, and your Alvin and the Chipmunks/Princess and the Frog argument just doesn't really work. But if it did, with Alvin vs. Princess, Alvin had many things in its favor that Princess did not. Even though the first was a critical flop, it was a sequel to a high performing movie, that earned its box office over a long period of time, while Princess had the bad pedigree of recent Disney animated movies, as well as the idea of a Randy Newman musical working against it. Yogi Bear and Tron don't really go along with that match-up.
I think of the three that open the next week, True Grit may be the biggest spoiler. Gulliver could turn out to be something, but I've not really seen much advertisement for it, and the same goes for Little Fockers. Little Fockers also has, ironically, the amount of time between sequels working against it a bit, while the second was a big hit, it wasn't a critical fave, and I don't think there has really been a big call for a third for a few years, so they may have missed the boat on this one.