So, maybe let's go back at the topic at hand.
I think the lack of use for Gold and Treasure is a DM and DMG problem.
First the DMG:
When a new DM reads the DMG (I did!) he is not told, how much Gold characters are expected to find per level. There are treasure tables and stuff but what is actually missing is just one small table:
"If you follow the treasure tables of the DMG, a character will find on average 100 Gold during Level 1, will have accumulated 650 Gold at level 5, 16.500 Gold at level 10 and 800.000 Gold at Level 20."
Because if you don't know how much Gold they find, how are supposed to be able to plan in how they spend that?
For my first big campaign I run I made my own table. I just said: Okay, the characters will gain money per level as Gold reward = XP × 2. Than I set the prices for stuff accordingly.
Like, okay, I now know how much money the party will find around level 5 (accumulated 13 000 Gold). At level 5 I want them to be able to buy 1 uncommen / a +1 magic item each. So for a 4 people group party, one uncommon / +1 magic Item was set to around 1500 Gold pieces. And I did that for all the levels and in regards to magic items and consumables like healing potions and it worked totally fine.
So to come up with a system to make Gold matter is actually simple:
Step 1: Decide on what the characters should be able to spend money in that campaign and what level those things should be available: Mundane adventuring Items (all affordable at latest level 5), Magic Items (+1 at level 6, +2 at level 11, + 3 at level 17), Strongholds, Followers, Ships, Businesses ... (and Talk at session 0 with your players about what Subsystems they want to interact with. Like, Magic Items always work, but having Strongholds and followers is not anybodies cup of tea).
Step 2: Just make up any Rewards System you want. Just determine how much Gold the party or a character will get per Level (which should be increasing by level).
Step 3: Set the prices of the Objects from Step 1 according to the Gold rewards set in Step 2.
Voila.
And such a simple system with guidlines should have been presented in the DMG.
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In my current campaign I'm a player in, Money is always tight. Why?
It is a city campaign. Two factions are now starting a war about the control of the city. Our adventuring group hates both factions and now we are becoming the third faction.
Even though I'm running around with 1000 Gold in my pockets, I'm feeling broke. First of all: My character is a wizard and getting all those spell scrolls and copying them is expensive.
Second of all: Write are building up a militia. My character made friends with a Velociraptor Merchant and wants to build up her own Cavalry made up of Orphans who ride on Velociraptors. That cost a lot of money.
We are campaigning with the people, giving out money to help the poor to have them on our side.
Money is Power in such a campaign setting and our (highly irregular) troops need to be fed.
The other campaign I'm DMing is a Spelljammer Campaign. The players have an Asteroid Hopper (basically a raft) as their first ship, which they are upgrading for a lot of money.
And later they will be able to buy more expensive ships and upgrade them, too. Ship campaigns like Spelljammer or Ghost of Saltmarsh have built in money sinks.
Like, I literally never had the problem of player's having to much money in any campaign I run or played.
The big problem is: The DMG, except for very wide price ranges for Magic Items, doesn't give you any guidlines on how to do any of the things I just mentioned.
Xanathar tried, but has anybody ever really used any of the Downtime Rules of Xanathar?
No? Me neither because in modern game play, Downtime of weeks or month barley exist.
Of course you could live for several month or a year as an Aristocrat, having 3000 Gold living expenses. But who really does that?