Not talking about XP here.
I'm talking about how the quest "In the Demon's Den" is actually VERY different at normal, hard, and elite.
For those that don't know this quest, you enter a demonic cave where a Marilith is trying to do a ritual to summon more demons to fight for her. She is being protected by a forcefield sustained by three elder efreets, and you need to defeat the efreets before you are able to defeat her.
At normal, she sit on the altar, and only after you defeat the efreets, she goes after you.
At Hard, the second you are spotted, she starts to chase you down. You can't damage her while the efreets are alive, so you need someone to keep her distracted.
At elite, not only she gives chase, but the efreets are revived if there are other efreets alive. So, you need to get rid of the efreets at the same time. Some people split up (like Tempest Spine's Fire and Ice), others pull the efreets to the center for the kill (like Shroud part 2).
A small change to the quest, but it changes completelly how you should run it. You can't get a group for normal (let's say, without a tank), and run hard instead, because you have to account for the marilith chasing you.
There is at least two other quest that changes on elite: "A Small Problem", the first quest on the Phiarlan Carnival chain. On elite, you need to fight the demonic wolves that were keeping an eye on Brawnpits this whole time, while on the lower difficulty settings, just there is no endfight. "In the Flesh", the last quest on the Harbringer of Madness chain, also features a very different endfight if you go on elite because of all the beholders around removing your buffs.
We need more quests that are harder not because of inflated numbers, but because there is something there that makes you life harder. Eg, on "House of Rusted Blades": Run on Normal, and you only need to rust the Blademaster's weapon. Run on Hard, and you need to rust every weapon rack around. Run on Elite, and you need to rust every weapon around and defeat the matron.
More objectives isn't the only way to make things harder. Adding traps, different mobs, or simply changing some spell selection/elemental damage around makes the quest kinda unpredictable, in the case you are distracted. Let's say, that fire trap on "Kobold's New Ringleader" could deal fire, cold, or acid damage, randomly. The Agility Test on "Crucible" might spawn illusory spikes instead of their normal blades (requiring will saves), or throw some very dangerous almost-instant poison damage (requiring fortitude saves or neutralize poison buffs), since the test itself is based on speed, and not evasion. You might need to see the traps before choosing who will run it.
Some more uses for Religious/Arcane/Wilderness lore might be useful for this too. Like adding a neutral NPC at the start of "Purge the Heretics", and if you have religious lore, might even turn the quest into a dialogue chain against the bosses, where you try to convert them to the Silver Flame. If you have enough skill for it, you got good XP without fights. If you fail, you trigger the current quest, where the devouts try to defende themselves against you.