I first celebrated the death of "wealth by level" structuring with a drink. Then I observed that yes, players accumulate wealth and D&D isn't designed to use that wealth to buy bigger and better magical items. In AD&D, you'd buy a castle, finance your army, pay your butler, open a thieves' guild, and so on. If you're looking for rules on that, recommend the "Pathfinder Ultimate Campaign" book (OGL is largely free online). It has a complete set of prices and rules for that type of stuff, and because it's a mini-game within the game, there's no conversion issue. You can run it largely as-is.I'm curious how other people have made the transition from more structured magic item and treasure editions like 3E and 4E over to a looser system like 5E.
I've run RHOD in 3.5, and it's got a timer, so lugging around hoards of coins isn't really what the adventure is about. I roughly have been knocking 3rd/Pathfinder conversions to around 10% wealth and making rough use from Xanathar's about how many magic items should be in my campaign. If the players have accumulated items they can't use, then use this as a roleplay opportunity to find others who might be willing to trade for something they have. Or, let them use their wealth to buy a treasure map or research a "recipe" into making an item.
Lecture Part: Just be aware that with the rarity of magical items, most people should be loathe to give one up. They should be an awesome thing to find (holy crap, a magical weapon?) that might redefine how you play your character. And if they aren't rare in your setting, then they aren't as special, and that was a major issue raised constantly on the forums when I played 3.5 and Pathfinder.