there’s experience in them thar hills

GET OUT OF MY WAY, IT'S MINE! MINE! ALL MINE!

Here is an incomplete list of things that “XP for Gold” does:

1. Makes treasure more desirable than its mere cash value
2. Strengthens the motive to seek out lost treasure troves.
3. Creates conflict between the player-characters and defenders of said treasure trove.
4. Turns dungeon delving into a caper film – “Arneson’s 11”.
5. Gives a further incentive to avoid (unprofitable) combat.
6. Ranks monsters on profit-to-threat ratio: troglodytes are the proverbial Citadel of Millionaire Babies.
7. Makes player-characters insanely greedy little devils – think: Daffy Duck level greediness.
8. Creates ironic distance between players and their wildly money-grubbing, cowardly, sociopathic characters.
9. Establishes that D&D is silly, maybe even preposterous, fostering a tongue-in-cheek attitude.
10. (If used in conjunction with carousing rules, opens up dozens of new story hooks, plot twists, and NPC’s.)

Could an alternate advancement system meet these same goals more efficiently?  Perhaps.  Could an alternate advancement system meet different goals?  Certainly.  But it’s a pretty versatile little rule.