Wondering what people will use when their inspiration/intention starts to lag/fade?
Goodman Games' Dungeon Alphabet, Monster Alphabet and Cthulhu Alphabet to the rescue for me.
If I find myself just going "bleh, it's a room with some skeletons," I will reach for Monster Alphabet and roll on the skeletons page until something inspirational comes up. Similarly with "it's just some stupid temple room."
But I also think it's worth reiterating McCoy's advice: It's OK to have empty rooms. If you are sending your players into a "dungeon" with 365 rooms, they will
need empty rooms to be able to camp, heal up, potentially barricade themselves in when they're being pursued, etc.
And depending on what your theme is, the rooms without active threats can be the most interesting. Maybe that's where the clues to the next challenge are. Maybe it's where you have to complete a task you've pieced together. Maybe it's the landing spot for that surprise drop down two levels when the halfling accidentally triggered a trap.
Given the number of levels involved, it's also worth thinking about dungeon archeology -- are all of these levels built by the same people? Are some of these repurposed? A few levels of caves is a good way to break things up, for instance.
And if you're making multiple ways in and out of the dungeon and each level, just connecting those up should keep things somewhat interesting, especially if you don't just randomly have those happen in corridors -- those seem like points that would be more likely to have some sort of guardian in place than others.