Yeah, you're right on the money. I don't think the sleepers are a non-issue, though. They're not like "regular" criminals; they're suicidal, murderous fanatics. Without the Head and Central Nervous System that al-Qaeda provides them, they certainly wouldn't be able to pull off another WTC, but they're still bent on their original goal. A suicide bomb in a bus, in a pizzeria, whatever -- small-scale attacks that'll take anywhere from a dozen to a hundred victims with them. If there are 10 such sleepers left in the U.S., that's one thing. What if there are 1,000? Who knows.
Sorry for the fearmonging
BTW, whoever said "I don't live in fear, but it's always nagging me in the back of my mind" -- how is that not ``Living in fear''?