Thanks for writing in Brian. Anyone who has a question, feel free to write me at valis at oook dot cz. I love getting mail and answering questions!

I've been entertained since I received this question!

If your monsters are wise, then they probably invest their money. I'm pretty sure the question is asking what sentient monsters do with their treasure though. 

If your monsters are intelligent in the same way humans, dwarves, and elves are, then they likely do the same thing with money that those races do -- they use it to hire labor, buy arms and food, and meet their needs. If they are a race with a culture that is intelligent, then they recognize that the money has power. If you're not particularly bright and you can't figure out a way to use the money (e.g. ogre), you would still horde it because your intelligence allows you to recognize that the money has power, even if you don't use it for anything. 

As an aside, I have spent years working with extremely low functioning people, with IQ's below 80 and GAF scores that required constant aid and supervision. Every single one has had a plan for getting wildly rich. "I'm going to move downstates and play basketball.", "I'm going to become a fameous rapper", or even "I'm going to wrestle in the WWE!". Every single one of them desired money as a primary motivator in their life. 

I really think what the question is asking about is what about intelligent creatures that are monstrous. Why would an umber hulk or an intelligent spider have money? I think that is an excellent space to inject the fantastic. Perhaps the umber hulk excretes the gold. Perhaps the spider breaks it down and uses it in the web. There are tons of fantastic and magical reasons why bizarre creatures might need or want traditional treasure hordes.