Your concern is exactly why the tagged individual is so much more powerful. You don't need anyone to sift through it to break people out or more people to follow more people - it's all automatic and just becomes a numbers game. Someone can go back afterwards and look at an individual if they want to - but the computers just churn through it all efficiently .
There is value in both aggregated activity and data of an individual. They have different uses
This point suggests that it's time for a statistics lesson to give everyone an inkling of how this stuff works. I use the word inkling because that's how much I know about specifically what Disney might do. While I'm not a statistician I do create statistical models at work.
The whole point of the data gathering is to create a predictive statistical model, and I'll explain just what that means in a minute. The model is derived from input "descriptors" which can be just about anything. Some of these descriptors are just raw data, like what hotel you are staying at or what land you are in at 10am or how long you you sit at a certain bench. Not all raw data will be used directly as descriptors, because some descriptors are derived (calculated) descriptors, like how fast you walk between the turnstiles and the hub. A statistical model is a way of using these descriptors from a large population to predict a "specific outcome", for example buying an extra-large Goofy plush, and in general you don't know in advance which descriptors are going to be important for predicting the outcome.
Theoretically thousands of descriptors can go into the model, and in general more is better because again you don't know in advance what is going to be important. Then statistical techniques are applied to find what weighting of each of the descriptors "best describes" the specific outcome. And by "best describes" I mean not just who is most likely to buy that plush, but also least likely, and everything in between. Every single descriptor will contribute to the model, just some will contribute much more than others, and the model tells which ones are most important. Some important descriptors will be things that weren't otherwise obvious, and some won't be important by themselves but only in their relation to others.
So where does NGE come in? Obviously, first it is a way to provide many more descriptors, both raw data and derived, and hopefully some of these will be important ones that produce better models. Second, and more importantly, the specific outcome must be known for all the individuals that are used to create the model. In other words, knowing all the data in the world about someone EXCEPT whether or not they bought that Goofy plush is worthless when it comes to creating the model. A subtlety here is that it is just as important to know who didn't buy the plush as who did. NGE allows Disney to link descriptors (lots of them) with outcomes in an unprecedented way.
So how is the model used? Creating the model requires aggregated information (descriptors and outcomes) from lots of people. The models keep getting refined as you add more people and descriptors to create new models. But once you have a model it's value is that it is applied to individuals to predict their behavior. This doesn't require thousands of cast members keeping tabs on us as individuals, it is all done automatically to us, as individuals, just as soon as enough data is gathered on us, as individuals, to have the input descriptors for the model. And at that point our behavior, as individuals, can be predicted and the targeting can begin.
But to me the most insidious part of this is that armed with a model Disney can use it to try to modify our behavior. To give a far fetched example, suppose that the models show that the descriptor "length of time sitting at a particular bench" is important to the outcome of buying that plush. Disney can put some small interactive element there to keep us sitting there longer, hoping to lead to more plush sales. Now of course some descriptors are not causal, like this one probably isn't, but some will be. The temptation will be great to try induce "proper" behavior of guests relative to descriptors, in addition to traditional things more directly related to the outcomes, like discounts.
So not only will Big Brother be watching us, they will also try to be using mind control on us.