Increased sales are easy to demonstrate. Just watch the 10Q's PRGS and PCGS numbers for the next 4 quarters and compare them to the last 3 years, which have averaged about 7-to-8% increases since 2011. In other words, that's the baseline increase before MyMagic+.
In order for MyMagic+ to begin to justify its tremendous investment costs, Disney will need to see double-digit increases in the PRGS & PCGS numbers, higher hotel occupancy, higher attendance, or a combination of all four.
In terms of 'savings', so far, Iger & Rasulo have reported about $300M more in added operational cost associated with new initiatives, which is mostly the result of MyMagic+. ("And this year, we're looking at about a $300 million expense item, and more or less the same amount on the revenue side.")
In addition, they have reported steeper-than-normal depreciation costs associated with MyMagic+. MyMagic+'s technology ages a lot faster than a brick-and-motor attraction.
So far, MyMagic+ has saved zilch.