Fotget about the treasure and pricing system of 5E!

[KorvinStarmast]

Agreed, and my only response is that various TSR edition games did have price lists for luxury goods, commodities, "dancing girls," and so forth, and at least 51% of the gaming audience seemed to have considered it fill material one flipped past to get to the crunch part of the game.

I don't know where you came up with that percentage, since at our tables we used most of the tables, eventually.

D&D is burdened by having multiple audiences (whom often have directly contradictory expectations)

To include a lot of video game players who don't understand recursion. (Yes, I may have started in D&D but I enjoyed me some Diablo, I did!)

I thoroughly hope that eventually there is an official 5e "Castlebuilders Guide" or somesuch.

Yeah, the 2e castle building book was pretty good. Would love to see a 5e version of that.

What's wrong with the current pricing of magic items? I enjoy seeing my players scrape together every scrap of wealth they have acquired to buy an Oathbow for the Ranger after the merchant agrees to sell it at half price for a favor. Why, my players just walked away with one rare and two uncommon magic items, plus a healing potion. It only cost them everything they had and some solid rolls, and now they feel much better going into the last leg of the campaign, where told riches await (told riches are much more reliable than untold riches).
I like how difficult it is to acquire a decent magic item. It makes them much more rewarding when the players get them.

Amen, deacon.

To answer the OP:

High level spells cost you gems. Take the gold and covert a lot of it to gems to be Used During Play when casting those spells that require gems.
Let me offer you a few examples of spells with expensive components:
Awaken: 1000GP gem
Augury: 25 GP gemsticks/tokens/etc
Contingency: 1500 GP gem/statue/ivory
Heroes Feast: 1000 GP value gem encrusted bowl
Imprisonment: 500 GP per HP of the target depiction of; the bigger the target in CR, the more expensive ....
Magic Jar: 500 GP gem
Simulacrum: 1500 GP worth of Ruby Dust
True Resurrection: 25,000 GP diamond dust
Resurrection 1000 GP Diamond
Raise Dead: 500 GP diamond
OK, I hope you get the picture.

The other thing GP is good for is paying for information.
Where can I find a magical sword? Well, after spending a bit of money on bribes and on a sage who specializes in history, we find that on an island in the eastern ocean is legend of a sword called flame tongue in the hoard of a blue dragon ... the only way to get a ship captain to get you close enough to that island for you to plunder it is to pay him 15, 000, since he's worried that this voyage could be his last should the dragon be awake ...

Here is my assessment of your actual problem.
You don't lack things to do with gold, your table collectively seems to lack imagination. (DM included)\

This Isn't A Video Game.