Okay, so in the classic forms of D&D, money equals XP. I'm not going to debate that or the mechanics of that. That's fine. The problem that I encountered back in the day was that players would accumulate more money than they could spend. My players were never all that interested in building fortresses or whatever. Now, we didn't have systems for "training" and "upkeep" and that sort of thing (never really crossed our 14 year old minds). It is possible to create "realistic" systems to deal with the amount of gold that PCs can end up amassing. And that's fine. But I'm not sure it's the kind of "resource management" I like to do (I'd rather deal with figuring out if the PCs have enough torches, oil, water, whatever while adventuring...I hate all that "in town haggling with the armorer" stuff...).
Anyway, so that's not really my cup of tea. Gold ought to be just another resource - not a means to gain levels (in fact, I'm toying with a system of level =x game sessions that someone online posted a week or two ago). Gold could be a reward for an action, that's fine. But there are lots of other ways to reward PCs, and they don't have to be tied to that which advances their level.
I've been reading the Conan stories. Sometimes it's wealth that motivates our favorite Cimmerian (Tower of the Elephant, for example, or the Servants of Bit-Yakin), sometimes it's revenge, sometimes it's defense (I'm thinking of Beyond the Black River here). Well, you get the idea. Even when money IS the motivator, like Tower of the Elephant, Conan does NOT do what your typical D&D character does. He doesn't knock on every table leg seeing if it's hollow, scoop up every copper piece and pry out every diamond chip from the idols. He's going after the BIG score, and leaving the "lesser treasures" alone. Why? He's not worried about leveling up (okay, that's not really it - he's way more into bragging rights, but still...this is D&D we're talking about, right?)
I'm not sure how to implement something like this in play. I guess you have to know what makes your players tick and play to their motivations. We're in a pretty greedy society, so most people ARE motivated by money, it's natural to transfer that to our games, I guess.