I've just started running Age of Worms in our 16 year campaign with Level 10-13 characters. The first couple of mods are way too easy even if you bump up the npcs and monsters a bit but occasionally I advance a monster to the maximum to lull them into a false sense of security.
I agree that, even starting at level 10, I think it's highly unlikely that they'll reach level 20 if they play the mods straight through but that might have something to do with the fact that I divide all xp awards by 4...
I'm planning to intersperse other mods in between with a view to finishing up with the final part of Age of Worms followed by Vecna Lives. I'll have to make Kyuss and Dragotha a bit less tough but I can always use the Black Dragon version from Wizards online supplement and help them out out in the final battle with a few other powerful magical items.
Bottom line is the mods can be fantastic tools for inspiration although in most cases they'll need some editing to fit into any home campaign. They're well worth it.
