I can't delete or move files in my Wii U's system memory - Solved! Thanks for the help!

[episteme]

Hm, doesn't sound good... Let's hope that the internal flash memory isn't damaged.

Maybe the Tropical Freeze patch failed to install, look at your download management to see if it is still there.
And check if the game updated to the newest version 1.1.0.

1GB USB sticks are usually pretty old and oftenly only have around 10 MB/s, but Wii U games don't work at that speed. Do you really have nothing else? I have dozens of USB sticks and external HDDs...