I got tired of it in 2013. While it does work in some places (Android does it reasonably well), I haven’t yet seen a good flat design on the desktop.
Windows 8 and 10 looked garish and hard to read, especially since everything is a rectangle with a one-pixel outline. Is it a button? Is it a text field? Maybe a thick progress bar? Who knows, they all look extremely similar.
While Apple did overdo it in the later big-cat OS X releases, I’ll take a felt-textured widget panel and a calendar bound in leather over an endless sea of hairline rectangles.
I think you’d like how Exalted handles money. (Note: I’m talking about second edition here; I never got familiar with third edition.)
In Exalted, wealth is represented by a Background called Resources. Backgrounds are essentially stats that represent useful things your characters has in a general sense like wealth, fame, contacts, or a mentor. They go from zero to five.
Resources is a vague representation of wealth. At Reduces 1 you’re one meal away from total poverty. At Resources 5 you have something that passively generates substantial amounts of money for your character, whether that’s ownership of a lot of land or an army of accountants maintaining your investment portfolio. Whatever is is, it works without you having to deal with it.
In terms of game mechanics it’s easy to use: Prices are expressed as Resource scores. If you want to buy something you just compare your score to the item’s.
It’s a nice system for a game that doesn’t want resource management to get in the way of epic adventure.