From someone who has played GTA III-GTA V, and every title in between without cheats; I've always experienced that quite first-world problem:
What the hell can I do with all my money?
Buy clothes in more recent titles that range in the 2-4 digits when I have several million dollars, buy guns I get given in missions and usually find ammo for for free, buy vehicles that I can only keep until I destroy them (which happens a lot...) or aircraft or watercraft I can already obtain for free easily.
San Andreas, Vice City, Vice City Stories, and GTA V had property. San Andreas property was additional save points wth copy/paste interiors, you really didn't need too many. VCS probably had the best take with upgradable crime ventures, but the constant attacks on them made them more trouble than they were worth ("Don't mess with The Sharks!")
Vice City's ventures were necessary for story progress, difficult to consider them.
And GTA V: More legitimate ventures like restaurants and theaters which you can't enter, receive menial benefits from buying, have to do work for, and see the return of your investment after several-hundred in-game weeks.
So what have we been able to buy? Cheap clothing and weapons that can be found, certain vehicles that don't necessarily need to be bought or customized, and property that only serve to give the player more money to do nothing with.
How can this be avoided in GTA VI? Does it need to be?
1) You could unnaturally raise the price of everything in the environment. A game I play, PAYDAY 2 is a game focused around bank robbery, so your money is obviously in the several hundred millions.
However, the cost of weapons, leveling up character skills, and jobs to take are also in the millions. A sniper rifle is $900,000. Bringing extra body-bags to a heist can be $10,000 for a Hefty bag...
This sounds like a cop-out, but there's something interesting PAYDAY does. The prime focus is on skill and leveling up, not necessarily just buying all the guns or skills since that's an easy endeavor. You need several hundred million dollars to do their form of "prestige", adding bonuses to your character. Perhaps GTA could treat money more like a points system in that respect. You can only simulate a certain amount of crap you can buy and enjoy in a virtual universe. Why not give the money a purpose similar to Vice City and being a necessity to progress either within the story, or to a new activity: like the boat races, cab drives, pizza deliveries, strippers with nicer polygons, etc.
2) Stop the frivolity with the mission payouts. You gain money for pretty much every mission you complete in GTA. Like points. Though, those dollars aren't treated like points, as mentioned^. Why do I get several thousand dollars for saving Roman from kidnappers? Did someone have that in their wallet who I killed? Keep mission payouts where realistic, and keep the payouts realistic. Why is Franklin complaining about being down on his luck and never getting what's his? You have several million dollars, buckeroo!
3) Does it matter? Are you bothered by your excess money you can't do anything with? Is the pursuit of money as important to you as it seems to be to the character?
Just a few of my thoughts. It's often debated but not much is said on it. Thoughts?