It’s probably semi-heretical in an OSR discussion, but there are things in OSR play that I think would be fine, if the rules weren’t as clunky or granular for no good reason. For example:
Wealth: Instead of tracking individual coins, why not track wealth as a general spendable pool, and if you want it to be more granular, you can attach tags like Negligible, Standard, or Bulky to wealth, to show how hard it is to carry. I’d also have a general note that if you have any wealth points, you don’t have to worry about buy X, Y, or Z, and that only comes up if you have 0 wealth.
Encumbrance: I think encumbrance makes sense for a lot of games, especially if you are trying to play into D&D’s tropes of getting rich and famous. The problem is when you have to reference charts or multiply stats and apply multiple levels. I with more encumbrance worked more like FFG’s Genesys, where you can carry X amount equal to your strength measurement stat, and whatever you are wearing doesn’t count against your encumbrance. I know this may not be 100% representative, but honestly, neither is D&D’s complicated encumbrance model in most editions.
XP for Gold: Instead of having thousands and thousands of XP between levels, I think XP would be more of a workable thing if it stayed in the single or double digits, and getting XP was more a matter of answering questions at the end of a session (like in a lot of PBTA games). Were we in danger? Check. Did we find treasure? Check. Did we explore a new place? Check. That’s 3 XP, and finding gold is part of the equation. (Yes, you could make the question more detailed, I just wanted to throw out some examples)
Alignment: Alignment is a pain in the ass, but I think a lot of the problem is that somehow instead of being an inspirational code of behavior, it became a label for what your character absolutely IS. I think if alignment were a non-binding idea of what the character WANTS to do, rather than what they automatically always do, it would work great, and looking at the XP trigger thing I mentioned above, instead of a punishment thing for not living up to your alignment, it could become another XP trigger if you do follow your own creed.
Saves: Between Swords and Wizardry’s single save, or Dungeon Crawl Classics 3e port of Fort/Will/Reflex, I think both of those are better options than the really arbitrary classifications of saves from earlier D&D editions. The single save model also gives you a nice way to model random luck as well, if you have someone just roll the save instead of adding any stat bonuses to it.
Consequences for Actions: One of the things that I think might make “10-foot pole” adventuring more exciting would be if there was a consequence for failure, even of there isn’t a preset danger. For example, if you are searching a room with nothing in it, but you still don’t notice anything in the room, maybe you were so intent on your search that wandering monsters show up. Additionally, I think having more “non-initiative” encounters would be nice for this as well, like bugs infesting your food supplies, or sneaking things stealing gear, instead of straight up fights.