I have considered dumping XP for monster slaying, and may implement it in a new campaign.
I find treasure a fine "scoring goal" like those in sports. Again, it is not a reward for any isolated incident (just as there are no points simply for hitting or catching the ball in baseball) but rather for a composite of actions. The immediate reward for avoiding a fight is not suffering the consequences of getting into one.
In 4E, treasure by the book is more of an entitlement (and perhaps shorter on gold pieces), but still by default considered important. On the other hand, it looks as if the game is set up so that one could easily strip away the "fluff" of magic items and integrate their effects as character powers.
The allure of treasure reflects a common motivation of adventurers both in history and in sword-and-sorcery fiction. Gold, gems, exceptionally fine armament and so on are traditionally tangible signs of glory. It works very well in the Dungeon exploration scenario from which D&D gets half its name, and the Dragons of the other half are renowned for their hoards.
However, to the extent that the game's level progression scheme reflects literary antecedents, they are mainly "coming of age" stories -- and those are more common in "epic" fantasies a la The Lord of the Rings. In tales of that sort, the driving motivation is beating The Bad Guys.
That typically means a lot of literal beating, slashing, stabbing, etc., with little reason to avoid violence except as a temporary tactic to the end of wreaking worse. If the game is primarily one of war (against Pure Evil, no less), then understandably a body count may be the chief way to score points. I find such a scenario too constraining for my taste, but of course tastes vary.
One can still get a lot of mileage from the basic principle of "XP for treasure". That is, there are objectives to attain (by whatever means the players contrive), securing which scores points. That allows one to avoid "pixel bitching" over each little action, quibbles over what constitutes an "encounter", and so on.
Indeed, this is often used with geographical objectives in strategic war-games. Capturing places of positional, political or economic significance can be a key means to the end of victory.
In other words, treasure is a sort of in-world "token" for the game construct of experience points. It is not at all necessary to use the same representation in order to use the same kind of distribution.
Rescuing Prince Constantine can be worth so many XP, driving the Pirate Queen Valeria from the Gold Coast so many more, winning the alliance of Graustark with Ruritania so many ... whatever suits the style of your campaign!