If play is intended to be both gamist and simulationist, then I think gold for xp only works for certain types of character, those who would be motivated by treasure. It works for PCs who resemble sword and sorcery protagonists, such as Conan, but not high fantasy heroes such as Frodo or Sir Galahad.
If play isn't simulationist then you don't care about how inappropriate it is that the cleric of Apollo is scrabbling about in the muck, looking for silver pieces.
EDIT: Though I think I detect quite a cynical attitude towards members of the priesthood in Gygaxian D&D. Vance, Clark Ashton-Smith, to a lesser extent Robert E Howard, all present a cynical view of humanity. It's common in sword and sorcery. So maybe the Apollonian cleric's behaviour is not so inappropriate after all.