Let me start out by saying I've never liked 4E's economy at all. Do YOU go around carrying thousands of dollars in cash in your wallet? Does it make sense to have a less technologically advanced society than us minting vast quantities of standardized coinage? And seriously, what's up with this 20% return rate? I can see in the math how it works out, but it's just so... contrived in a lot of ways.
This is one of the big worldbuilding issues I considered when preparing for my most recent campaign and one day at the lab, an idea struck me. Now that I've seen it in play, I can't imagine running 4E (maybe even 3E/Pathfinder) without it ever again.
I cut the PCs actual gold earnings to about 10-20% normal (this will decrease even more in Paragon/Epic tiers) and then put the balance in a sort of virtual “bank” in two separate “accounts” – one called Fame and the other called Karma or Luck. PCs can call upon this bank to obtain needed goods and services. For example, rather than actually shilling out 100 gp for a Raise Dead ritual, 100 gp is subtracted from the character’s “bank” and the priest performs the ceremony because the characters “have done such good around here.” The “bank” also represents resources funneled to the characters through their various sponsors, benefactors or investments. In practice, there is little mechanical difference between this system and the default economy – it is simply flavor to further illuminate the game world and allows the PCs to throw around their status as famous adventurers in a measured, regimented way.
Karma or Luck is earned for performing actions that help restore the natural “correctness” of the world. Noble deeds, delivering justice, killing undead, pretty much anything stereotypically “Good” earns Karma. It can be spent like normal GP in stores representing the odds that the location actually has what the characters want. It can also be spent while adventuring to have certain events occur. For instance, spending 50 Luck in a dungeon can give you a Healing Potion as treasure in the next encounter or chest. Spending 20 Luck can ensure that a water source you find is pure (as the Clearwater Solution). As a general expectation, the cost of an event is equal to an item that causes the event.
Fame is earned for performing deeds that will be talked about by others. It can be spent like normal GP in stores representing the shopkeeper's willingness to sell the characters rare or dangerous items. It can also be spent while adventuring to have certain events occur. For instance, you can use Fame to “bribe” someone into letting you into an area they shouldn’t. It can purchase room and board in foreign towns when you lack the on-hand gold. (“Hey, we’ve heard about you guys? Tell us about your travels! A place to stay? Sure, it’s on the house.”) PCs might also spend Fame to receive gifts and favors from NPCs that they meet. As a general expectation, the cost of an event is equal to an item that causes the event, though this isn’t quite as sturdy an expectation for Fame as it is Luck.
When a PC goes to buy something, he or she is only required to have a fraction of the cost in currency. The rest is paid in Luck or Fame. Thus when he or she tries to resell it, only the currency is returned and the 20% number makes more sense in-game. It also eliminates the problem of a single +2 weapon costing as much gold as a small army. The army only needs gold for food and supplies. The weapon requires Fame and Luck, which most NPCs do not have. I've found, as a side effect, that the system additionally tends to (though not completely) keep the party moving on the straight and narrow since they know the sorts of things that will earn them full wealth – big, heroic deeds. It would be just as simple to change Fame to Infamy if I was running an Evil campaign or Karma to Honor if the players were of a culture where that sort of thing is important.
Combines with the automatic enhancement bonuses, the system has served me well so far and I foresee it being even more helpful given the magic item changes, particularly as it functions as a sort of compromise between the 'wish list' and 'whatever the DM puts there' methods of treasure placement. If my players are going to have thousands of 'gold' to just throw around, I intend to give them ways to spend it.