Basic Fantasy (a Basic D&D Retro Clone) has the XP for Gold optional rule: 1 GP of coin or treasure returned to a safe place rewards the party with 1 XP. This is in addition to normal XP rewards. ...
I really like my good ol' Moldvay Basic D&D. Every once in a while, it's missing a rule I want, and I make it up. Then I feel clever. Sometimes, though, I want to know what everybody else did ...