The problem: The eShop was erroneously declaring that I had insufficient space available, which prevented me from downloading a particular piece of software off of the eShop.
Whenever I would attempt to download Disney Infinity 1.0, the eShop would notify me that I had insufficient space to download the game. In doing so, it would call out my System Memory as the destination, which on Wii U Basic Set (with 8GB of storage) was obviously incapable of housing the 9.6GB required. However, I have attached a external USB storage device, which had 50.2GB of free space -- plenty to store the game. If I perused the software catalog and attempted to download a game which I had not previously purchased, even a large one (12.8GB for DKC:TF), the eShop would specify that the destination for this download would be the USB Storage Device.
Why would every piece of software call out the USB Storage Device as a destination and not this particular one (Disney Infinity)?
The cause: I had played Disney Infinity (off-disc) prior to adding the USB Storage Device, which has all the update and save data (which I will refer to as the “App Bundle”) on the System Memory. Because the Wii U System Software directs all storage activity to wherever an App Bundle is found — with a preference to refer to the USB Storage Device, for new software or even if an App Bundle is found in both locations (System Memory and USB Storage). As a result, attempting to download this app from the eShop would have the System Software treat this data much in the same way as if it were an update. That update would have to reside in the App Bundle, which was only found on System Memory and thus insufficient to store the entirety of the applications’ data.
The solution: In Data Management, move the App Bundle from System Memory to the USB Storage Device. Returning to the eShop, it now considers the USB Storage Device as the destination — no longer considering the System Memory at all. Yay! It doesn’t matter what the software is (I validated this solution by also attempting to download Just Dance 4, which I had played off-disc prior to adding the external storage), if the App Bundle for what you want to download is already on System Memory, it may likely be insufficient to store the game’s data. Move it to your USB Storage Device and all will be well.
The reason: Had I played Disney Infinity after adding the USB Storage Device, the Wii U would have defaulted to storing the App Bundle there. As a result, I would have been blithely ignorant of this issue, because the System Software would have downloaded the game data right to the capacious USB Storage Device.