I will say that the "subsisting on energy from a hoard" trick that dragons do isn't unique to them (although they're the big names in the business). One particular lich made (part of) his lair into an art gallery, showing off ancient and carefully preserved artwork and famous items. He fed off of the admiration and feelings of the visitors. Oh, and the occasional snack on the life-force of a would-be robber, but everyone cheats on their diet, don't you know?

Worked great, until magic went out/got broke for a while and the visitors stopped coming. Getting eaten by an intelligent, malicious thought form of Gluttony wasn't too good for him either. Thankfully some adventurers stopped by and nuked the Gluttony-spirit, freeing him to rebound through his carefully preserved phylactery. That gnome is back up and running now. Got out of the art business--now he's in the more traditionally soul-sucking field of education.