Get those diplomacy skills out. One of your PCs should be a tricked out diplomacy master who makes deals with local goblin tribes and such... instant cannon fodder! Pitch your plan to them... lure in adventures... adventurers who carry loot... kill the adventurers, or at the very least steal their loot. Split the loot with the goblins, keep some as capital. Remember: the larger your hoard, the higher level PCs you'll attract, meaning the more you can gain! A dungeon like this is like an investment portfolio, always with the slight risk that you'll lose it all...
And like any buisness, there are different plans you can use. You can try to attract the quality customers by pooling the wealth in one big location (with one big guardian!)... or you could scatter smaller pools of wealth throughout a larger complex, which I'll call the "WalMart" strategy. You'll attract a weaker adventurer, who'll have less gold, but hopefully there'll be more of them...
You should consider the effects of frightening off potential "customers" as well. If no one ever returns from the cavern of doom, either you'll be getting adventurers WAY more powerful than you're ready to handle just yet, or if you're too successful AND you don't have much loot to offer, you won't get anyone showing up AT ALL! So consider letting some leave with some trinkets... part of the investment. Consider it advertising cost.
Sounds like a fun game...