Keep in mind, Avatar reintroduced 3-D to the movie industry. The price of admission was raised for the 3-D and boosted their profits exponentially. There's a possibility that it may have been a one trick pony for 3-D. It's really difficult to say if that's the case though. We won't really know until we see the results of the sequel. Hopefully, it'll be good.

People flocked to Avatar more out of curiosity, and to see whether Cameron good deliver on his hype and promises. Now people know what to sorta expect with avatar 2, so I doubt it will make as much, but will undoubtedly still be a successful film regardless.

Yes, 3D boosted sales through higher prices, but there's no reason that won't be the same case with the next movie, especially if they meet the same standard or exceed it in the 3D field with expanded sights of Pandora, etc.

And I don't think you can say the movie won't make as much because the first one was based on curiosity to see if James Cameron could deliver. The opening weekend's numbers were based on that curiosity, which one could say were relatively modest compared to the ultimate tally the movie collected. In the end, Avatar went uphill, which is usually unheard of, and had amazing stamina at the box-office based on amazing word-of-mouth and popularity. It is true the box-office might decline because some people saw the first movie based on people's advice but just didn't like it in the end. Although, if Avatar 2 does more than rehash the same visuals from the first and offer a fresh story, it's not ridiculous to believe the second one won't exceed the first. I think the first movie's opening box-office weekend is a sure-thing to be beaten. The final tally is more debatable.