Finished what I started last night, and made my way into the Subterranean Complex cave in the Valley of Repose. First few floors were pretty easy, but then I had to kill some floaty things which dropped bombs, and some electric beetle things, and some spidery things, AND get rid of some poison clouds, all in the same three square millimetres. Lost a few Pikmin, but made it through.
Then had some big metallic thing that kept firing things at me to contend with, but managed, and picked up loads of treasure. By level 8 I was wondering when this dungeon was going to end. Stocked up on purple Pikmin from some flowers, and went down to level 9 to defeat (after a few attempts) a big metal spider with a laser. Erk. 45% of the way to repaying the debt now, which is the aim of the game.