I have a few problems with your suggestions:

1) This effectively creates a minigame where you try to stockpile healing stuff before major points. It slows things down and just acts as a nuisance.
2) I'd see this slightly differently - mana regeneration at 0-10 should be normal, 11-20 should be halved, 21-50 halved again. This would perhaps force players to use spells more sporadically and focus more on the balance between immediate need and future considerations. You could still frequently use quality of life spells like neutralize poison, light/dark or slow but double digit costs would make you think twice.
3) Tedium. Sorry but no. This is just not acceptable in any form to me. I already ID items based on weight or name before I use the scrolls and I don't feel compelled to overuse blessed scrolls because they're, I dunno, amazing. They're just out there and they streamline the gameplay without making it too easy.
4) I don't use arena food at all anymore. Stomafillia is a convenience feature but I want to keep it around. Instead, I'd incentivize using other forms of nourishment - dramatically decrease weight and increase satiation boost. This is another case of game within a game. I want to play ADOM, not Hunger Games.
5) Acceptable under the condition that the general rate of destruction of items is revised from the ground up. Anvils breaking when thrown against doors is just not acceptable and there are many similar examples. Corrosion and rust should never be instantaneous and rather work like the changing damage dice of the charged artifacts - unless the PC applies a cleansing oil, the weapon has a chance to rust/corrode every X amount of turns. If artifacts are made destructible then at least modify the code so they can randomly drop again after that.

I think I understand what you're saying about the game becoming easier and I have noticed that too. More content in general allows for RNG to really have more opportunities to shine. Getting to the young settlement and finding 10 potions of water which together cost 1000 gold is a game changer early on.
While I'm open to making the game more difficult, I don't want it to be tedious and that's where most of your suggestions are going.

I have a few ideas of my own which I think don't increase the tedium but naturally force you to be cautious:

6) Make traps deadlier and/or scale with DL. In the worst case scenario, spear and arrow traps are marginally annoying. I'd love to see them paralyze, cast darkness, penetrate armor and hit companions behind you when the PC is traversing the maze or the DH for example. Acid and stone block traps are already quite deadly, if only to inventory and health, respectively. Pit traps on D:40 and deeper should have eternium spikes that insta-gib strained and very strained players when they fall in. Nothing like a death message saying "got impaled through his anus with a barbed spike when his massive luggage dropped on top of him in a pit".
7) Smarter monsters! I have always said this, AI in this game is so stupid. Why not make projectile throwers back away from the PC instead of closing the distance? Why gorks* patiently enter bottlenecks to be slain one by one, instead of going around or clustering around the entrance to the room to swarm the PC? Why fire dragons waste time on breath attacks against PCs that are immune to fire and wear two blessed rings of ice? Why balors are so easily lured out one by one, thus removing their major advantage? Can't they communicate? We could keep on going. I could imagine one of the difficulty sliders to be "Monster AI: simple/complex", with the former being what it is now, the latter - a revised, deadlier version.
8) Make wounds and all forms of negative status effects, as well as damage to the player, have long lasting consequences over the course of thousands of turns. Stunning should abuse Ma, Pe and Le. Paralysis should abuse Dx and St. Bleeding should abuse To and so on. We already have some of that with very strained and overburdened so there's a precedent.
9) Increase the pressure of in-game time on the PC - after day 60, more purple stuff crawls out. Day 90, dwarftown gets invaded and jellied, all randomly found food is always spoiled, half the potions are "of chaos". Day 120 - all wilderness encounters are purple, towns get many random chaos monks turn hostile any turn and attack not just the PC but NPCs as well - eviscerate the tiny girl or stab the drunken dwarf. From here you can extrapolate day 150, 180 etc.
10) Characters carrying many items should be targeted by ambushes - if you have many scrolls, rings or potions, you get teleport-jumped by a bunch of rogue wizards bolting you from afar. If you carry a lot of swords, shields and armor, a cluster of disgruntled, destitute weaponsmiths, artificers, shopkeepers etc should take hammers to your balls when exiting staircases or turning corners. Lots of rations, morgia, spense and stoma - your eyeballs get pitchforked by starving farmers, butchers and wenches. I'm talking about the suddenness and rapidity of the pyramid scroll or water trident deliveries. Violent and in your face. Have raider lords with poisoned darts and trained para-ghuls and gorgons on a leash await every time you exit a random cave with a bulging bag of goods.

*G.O.R.K. - goblin, orc, rat, kobold

I feel like you're missing the fact that I was suggesting *options*.
Selectable items to increase challenge. Not balance changes. *options* for players to enjoy an increased challenge in ways that just putting 'rules' on yourself cannot achieve.

For example, lots of roguelike and hack and slash games get incredibly fun when healing is restricted, and I'd love to play adom that way.

If a player found it tedious, they would obviously just not select that increased difficulty option?!

Why exactly would that option be a bad thing?

I'd expect very few players to select them. Options or not, they are also proposed features and I evaluate them as such.