Stories are about people. And people are universal. A story about people can be set in high fantasy, or in a mystical modern urban setting, or ten thousand years in the future, and the concepts will still be the same. Sure, the greed in a person's heart may be for Phlebotonium instead of Adamantine, and the scale of domination may go from nation to world to galaxy to universe, but the underlying concepts will always be the same.
So when you're stuck for an adventure idea, it might be a good idea to do two things:
Firstly, take a step back and look at your adventure in the abstract. You probably have a few good personalities mixing it up - a few powerful NPCs (who hires you? who are your chief rivals, who are your enemies?), the PCs themselves and so on. Take a look at their desires, their fears, their needs and so on, and see if you can't intermingle them a bit. If NPCs want something abstract (political power), but can't get it directly, they'll try to acquire something that will eventually give them that. And that can bring them to rivalry or competition with another group, NPCs or PCs. Voila, conflict, and from conflict, drama, and from drama, adventure! Or if a powerful NPC wants something concrete (as opposed to the abstract), and it is not interesting to the players (say, a powerful wizard wants a spell, and the party are all fighters), you can quite handily make a common stepping stone for rivalry - a key to a horde of treasure.
Secondly, to take the old fiction and RPG writer's axiom - steal. Steal from anywhere and everywhere. Pick up a novel. Look at the underlying abstract desires and fears of the people involved. Change the McGuffin they want (political power in a monarchy) for something similar but different (advanced status in a guild).
See, on a slightly more mechanical level, a good model for human motivation is Maslow's Hierarchy of Needs. And it teaches us a lot about how to build compelling characters in RPGs. Of course, applying it universally is a bit insane: every minion and mook you face probably won't have a thought on this scale, but if a canny DM wants to flesh out an NPC a bit better, it always helps to consider where they're at in the hierarchy.
Take a look at most end-game villains for instance. Orcus doesn't care about safety! He's the biggest, baddest mother-lover in the valley, he fears no evil! Neither does Abaddon, or Caine. They're totally self-actualizing.
Comparatively, the average peasant in a hut somewhere is scrabbling for safety first, then food.
So let's play a little with the idea. Firstly, the idea works really well if you're messing with scale. What happens when a self-actualizing dragon interacts with starving peasants? A good dragon is defining itself, so it brings them food. Peasants freak out at the sight of the dragon, drop to "safety and security", and flee. How about an evil dragon?
Well, that's an interesting question. Alignment and personality have caused more arguments than I'd care to think about, but evil normally assumes some sort of greed and/or jealousy, which ties in to some sort of scarcity. An evil dragon would presumably actualize their evil by collecting stuff that is rare. Starving peasants may not necessarily interact with that need/desire well... but a little creativity can solve this. Perhaps a peasant has an heirloom. Perhaps the dragon needs something that a dragon can't get at - so he throws money at the peasants to steal for him. Now we can build an entire thieves guild adventure around stealing rare stuff for an evil dragon.
Esteem in the hierarchy is a particularly interesting one, because it tends to be vastly overplayed. Why does an evil person do what he does? He wants power, because he wants power. Who doesn't want power? He was once powerless, and now he just wants to kick ass. And it's great, because it's tropey, which means it's safe. Players "get" the need for esteem, which let's you all chill out if you want a nice, simple game. But if you prefer the intrigue of clashing personalities, the ability to play NPCs against each other, or just to flesh out a character more than "wants gold", I'd recommend thinking through the underlying needs and desires of your characters. It can make for some great adventure ideas, or even whole campaigns.