This originated from an ancient issue of Dragon magazine, but it's easily applicable to any OSR game. Rather than awarding experience points for the acquisition of gold, experience is only awarded for money "wasted".
Money can be wasted in a number of ways: Magical "research", donations to the church or the poor, an epic bar crawl or any other nonsense.
In short, anything that suits the character but does not earn the character any other in-game benefit. Thus money spent on hirelings, buying items, spell casting etc does not qualify.
Characters may burn money on training and magical research to earn XP, but only if it is "background training". In other words, actual training to reach the next level, or to add a spell to my book does not count.
This helps funnel money out of the campaign, and also helps make players have a few more decisions to make.
Try it out and let me know how it goes!