As many of you will recall most of the Korthos Island quests actually started as different quest and where then slightly modified (mobs, layout, xp, loot, etc) to flow with the new story line.
I would like to see Turbine do this to many of the current quests. Add a little flavor, change things up a little.
A few thoughts though.
1) I'm assuming this is much cheaper (programmers, etc) than making a new quest. If not, then probably not going to work
2) This idea works for me other player like me because we get enjoyment out of leveling and running new quests (I tend to TR a lot). Little changes would add a lot. This really does nothing for those that are more into loot/Epic running, so you would still need new high end content (thus point #1).
3) You would have to correct various risk/reward items you have that are way off (e.g. better rewards, less time, more xp etc) for some quests. (but you need to do this anyway, so have at it).
4) Low level quests are probably a waste. We spend way too little time at those levels. Mid level heroic content is probably where to start.
5) Be careful with the sacred cow quests or you'll have a riot on your hands (You almost have that now with buying time).
A handful of dungeons per update would be great.
As an added bonus you could then mark these quests with the cool recycle symbol