That's why OSRians started requiring players to actually spend the money before they got XPs every time they returned a case of Mountain Dew empties for the deposit. This notion has much more to offer, but, as it applies to demi-humans, I'd like to take it further; to do something with it that will make demi-humans feel more different from humans.
One of the prime differences between humans and demi-humans, I'm thinking, is their particular relationship with material wealth. Us humans, we like wealth for the power of buying whatever the heck we want, be it hot tubs, influence, chain mail, cock rings, what have you.
|This oughta' get ol' Blodgett up to 5th level|
For dwarves, the value of wealth is not the spending of it, but the hoarding. They derive ecstasy from the gathering and stockpiling of precious metals, gems and other products of the earth. XPs are not actually earned until treasure is safely stashed either in a secure financial institution, the vault of a trusted ally, or a dwarf's own personal storage structure; somewhere where it is safe from being spent. Many "dungeons" are actually the treasuries of dwarves of legend. Bonus XPs can be earned for transforming gold and gems into fine jewelry, ornamental weapons and other such eccentricities which can be given as gifts or worn about.
Halflings view material wealth as a means to domestic tranquility; as such, they gain XPs only for GPs spent on the acquisition and improvement of real estate. This ties halfling characters to place in a very measurable way.
As you can see, humans can drop their cash in G'hawk, Mordor, or Lankhmar, and it doesn't much matter. But for demi-humans, their wealth will be closely affiliated with a place somehow. Either in the grove of oak trees in Sherwood Forest that Melf has endowed, the treasure hoard and associated safeguards that Gimli has stashed under Mount Fuggitt, or the plantation that Poblo Fraggins owns in Aquilonia, demihumans have some sacred place that they need to be tend to. Or they can just forego XPs for GPs; which is fine by me.
PS. The photo was swiped from http://pinterest.com/wandans/hobbit-ty-homes/. They've got other photos of hobbitty places if you're into that sort of thing.