When I was gearing up towards running a 1e game for the first time in 20 years a few years back, I ended up re-evaluating a lot of the things I'd basically disregarded as either too-complicated or too-silly while I was growing up playing the game.
The most striking of these was the XP-for-GP system.
As a middle- and high-schooler, I thought it was the silliest thing I'd ever heard. How in the world can getting money make you better at your job? As an adult, with the help of a few forum discussions, I realized it's a feature of 1e that makes its playstyle unique among the various D&D editions.
XP-for-GP rewards you very directly for a smart, cautious playstyle. Monsters give XP when you kill them, sure, but that's piddling compared to the XP you get from escaping with a ruby necklace or a +1 sword. So, given how lethal combat could be, your best course of action is to infiltrate a dungeon, make minimal deadly contact with monsters, and escape with the loot.
One of the things Next could provide to get it close to 1e in my "top editions" ranking is by incorporating this as an optional module. It was one of the most eye-opening things about 1e for me, and it's one of the main reasons it's my second-favorite edition now.
-O