I am having the same issue. I own the Deluxe 32GB system, and if I were to delete all of my games the console will only have 13GB of free space (instead of the 25GB I should have). That isn't enough to download Smash on its own...
---EDIT---
Apparently I had a LOT of Miis stored within the Mii menu. After deleting those I had 18GB to spare, I just never imagined those little guys would be so space consuming...