This sounds like an interesting campaign idea. Let me think...
Well, sticking with what you said about running a colony, and expanding on what people said about being high level...
Assuming 4e, one of the game's conceits is that PCs are special. Everyone not a PC is an NPC and maybe even a minion. If one of the PCs for instance, plays a Wizard, he's likely the only Wizard even IN the colony. In any situation calling for a Wizard, it's up to him.
A gang of goblins causing trouble? The town turns to the party's Fighter, the strongest guy there is. Besides the party the only group who can even fight are the town guards, and they're only level one Human Rabble or something, only good for keeping the minion common folk from killing each other in bar fights. Not good enough to send out to slay a band of level five goblins or whatever.
In fact, let me expand on this another way. Let's say 4 PCs, semi-typical party... Fighter, Cleric, Ranger, Wizard. Not only are they likely the only ones in the colony above level one, as PCs something just makes them stand out more than normal people. In a crisis, people just naturally look to them for leadership.
The Fighter is head of whatever passes for a town militia or whatever, the military leader. When it comes to defending the peace or the town, he's in charge. Nobody in town fights better than him, since he likely taught them everything they know.
The Cleric? He's likely the head of whatever the town has for a church, the town's religious leader. Everyone else is just a laypriest, without any divine power. If undead show up or something, he's the only one who can smite them, and he's the only one with healing powers.
The Ranger (sorry, I was short on Rogue ideas) is say, the head woodsman and hunter. In fact, maybe he leads a group of rangers who prowl the woods hunting and scout around. (Aragorn for the win). He knows all the local dangers, and his men warn of when a band of gnolls move into the neighborhood. But his men are hunters and scouts, not good for more than killing deer. Only he can lead the party to the gnolls hideout safely, and help you slay them.
And as mentioned, the Wizard is likely the only guy in town who knows any magic. Maybe he's trying to take on apprentices or run the local school, but the party needs him to deal with any arcane troubles... heck it likely needs him anyway, having a Wizard along never hurt. If the party has to slay a dragon, you certainly don't want to leave him behind, do you?