Yeah, I'm late on this, but whatever.
Disclaimer: I can't speak for D&D, since I usually play Shadowrun, where no matter how tough you are, a couple bullets will kill you. Period. I also play Call of Cthulhu, where the monsters can kill you by looking at you, literally.
Anyways, I find that if you have a really good GM (or DM), it doesn't matter how powerful your characters are, you can't get through the entire story with brute force, more diverse skills and actual thinking are required. So the plot doesn't necessarily have to be scaled up. Again, that often applies to Shadowrun.
Also, and this is 100% personal, I don't believe in game plans, they tend to be too restrictive. It's more fun to give the players a fairly open-ended mission and let them work it out themselves. Hell, in the last Shadowrun campaign I played, our GM didn't even give us missions, he'd let us take care of ourself and occasionally throw a wrench in the works. We were all experienced players and had a goal in mind (expanding our corporation that we created), which made it easy and fun to have an extremely dymanic storyline.
