So, I was a little bored, and I'm a geek, so I went ahead and figured out exactly how the Magic Bands work, and what information Disney can actually get from them.
The bands have 3 RFID chips. 2 of them are passive (this means that they are powered by surrounding radio bands, and one is active (uses the battery to power a transmitter).
Chip A - HF band, passive. This is the standard touch-to-pay RFID chip found in credit cards and the like. In practice you must be touching the transmitter for this RFID chip to charge and disperse the information. Information on this chip is an ID code. This Chip is the same as the magnetic strip on the back of your KTTW card, just newer technology. If someone wanted to buy a reader for this, they would have to touch it to your bracelet and hold it there while the chip charged up and gave up the data. At this point the best the thief could do is to print out a new chip, embed it in a similar looking card, and spend up to $50.
Chip B - UHF band, passive. This is the creepy tracking RFID chip. The max range on this is 15ft, and the benefits for this particular chip is that you can read a large number of them at the same time, they are generally used for asset tags. This is to replace turnstile counting and otherwise measures the flow of people in the park (Unfortunately I have no idea if the cards will have this too, so in the future you may not be able to opt out of being counted as an 'asset'.). Because the read distance is so great, it is highly unlikely that this has any personally identifying information on it due to the fact that any
shmoe can go onto ebay and buy a reader for it.
The other thing this chip could do is like Pal Mickey used to, trigger offers in your 'My Disney Experience.' "Hey, it looks like you're wandering around Fantasyland, why not check out Mickey's Philharmagic? Here's a free Fast Pass+ so you can get in on the next show!"
Chip C - WiFi band, active. This is the little transmitter. It transmits up to 6ft, and likely provides opt-in personalized experiences (Cinderella says, "Hi Victoria, Happy Birthday!" for example). This particular chip is almost identical to the toll transponders you put in your car. Extremely likely that this is all encrypted data because it is personally identifiable (but in general, useless to a thief).
Thievery: Unlikely. It is far easier, cheaper, and more lucrative to install Credit Card skimmers. Thieves are not likely to zap your RFID chips and reprint them for use when they can instead take a Credit Card number and order a $2000 computer online without blinking.
Big Brother: Feels a little creepy. Well, what does Disney already have on me? My KTTW has park access, a number for biometrics, FP use, purchases, along with names, ages, address of my party. With the Magic Band they can also store the RFID check in points as I walk through the park, creepy, but what can they do with this information? Well, first of all, if I'm walking into a CS restaurant, I'm probably buying lunch and that will show up on my KTTW card, so that's not new information. What is new information is walking into a gift shop and not buying anything. So maybe they give you an incentive to buy something? A 10% discount if you go back today. It's 2pm and you haven't eaten lunch but are still in the park? Order now and your food will be ready for you at Pecos Bill.
Conclusions:
Really creepy to be an asset, realistically they already do track us, this gives them more accurate data. Offers and Personalized experiences are likely opt-in. I really hope Disney has a way to opt out of personalized tracking. And I better get a piece of paper at check-in that explains what they're using my information for!