Actually, thinking about it a little more, I'd like to suggest something along the lines of the following:
Whenever someone saw themselves in the mirror, they tended to do a slight doubletake, as if they knew something wasn't right. But that failed to re-awaken them. Why? I think it goes back to the theme of finding redemption individually, but needing other people to help you do it. That's why they had to interact with those that they loved, or in Locke's case had to be fixed by Jack.
Oh well, that makes my record for Lost theories about 0 for 400 while the show was still on the air, and now 0 for 1 after it finished

But worth a shot anyway...