well for D&D just add any non-D&D type rule to shake things up.
these sort of things work best in TSR-era D&D without nonsense like WBL and such where the party has more money than hookers and can set up their own stronghold or keep or whatever.
say they are traveling a ways off and you don't really have a reason for them to be damage in any way during the journey. maybe you are just tired of the bandit attacks and such....
As you set of on your adventure it will take 2 weeks to get to the city of Townshireville. the villagers wave by and the parade ends as you ride off.
now hand each of them a new character sheet of several of the villagers of their own keep that they will play while their real character are traveling, and these mundane characters will fight the bandits and critters while the PCs are gone.
YES it is different!, because not all the villagers have to live. they may have to spend some of the parties funds to hire help or even hire another adventuring party to help defend. who knows what really would happen, but it lets the PC players see that the lives of their stronghold denizens are real and not jsut set dressing and interesting as well. then when they return from the latest adventure and find newly built buildings or that their gold has been spent, they cannot blame DM fiat on the expense but themselves because they KNOW why it all happened!
this is also good for sailing voyages if you don't want to try to create some kind of naval warfare system, or if you just want to take a break from the big super plot of a game and play some lower level characters or whatever. just the PCs stronghold is ripe with adventure and intrique as well.
now toss in the "jamming" concept and add the "whatever happens goes" into full affect and you may have villagers leave the stronghold, or plot to overthrow the PCs when or BEFORE they return! but would your players really do this to themselves for the fun?
where systems have funky WBL, you cold just build another city far away an re-enact a scene from another game the players were in, but this time they are the major townsfolk and get to control them, while you paly their old characters and try to keep the game going in the way it originally did until they realize WHY it is they may be remembering these events.
these also work when you have an absent player, not just absent character. hell one of them might even be suggests in CC. this way the other players can keep playing without leaving Jeff out because he had to stay home with little Billy who is sick.
another idea for another town concept is fast-forward to a later town in the game that has a bunch of exposition and let the players play another set of adventurers in it that will die or something, but this will allow your players to SEE what happens as they wil be informed later when their real character reach the town.
DM: you ride up to Townshireville and the gates are busted open.
Player A: CAn we tell if there was a fight here?
DM: Remember back in march when Jeff had to stay home? This is the town you were all in and the event that happened are the same as then. ANY NPC you meet will tell you the same story you already know.
the plothooks were planted LONG ago for this area now.
now if you do all of these things it can get kind of interesting. have the PCs on the way to Townshireville while the players play their stronghold villagers for one week. then switch to Townshireville to let the players play out some characters there, and at the end of that second week...
"You see a group of people riding hard and fast towards the entrance gates!"
now the PCs have caught up to the town itself and get to switch bodies while the people they had just been playing become NPCs.
it can either be interesting or very confusing, or BOTH!