A clipped signal will kill a speaker over time. It wont instantly, but in time yes. When a signal is clipped it removes the curve of the wave on the top and bottom, hence the name clipped, and when it does so a tramendouse amount of heat is generated resulting in a burnt VC.
I **** at explaining things and have been to a few class' on the subject along w/16 years in the field. If I don't know anything then I wont post.
Bottom line is a clipped signal/distortion is the number one cause of speaker failure, yes due to overpowering. Call up any manufacturer of speakers and ask.
I can see this is going to be a waste of type so I'm done w/this thread.