In my installations I use surge suppression devices on the incomming line all the time. The MOV bassed devices do indead degrade with exposure and should be replaced every so often. The gas discharge tubes are very rugged but do not clamp the incomming transient at a low enough level to protect audio electronics. The recomendation of multiple locations of MOV based suppression is a very good idea. The MOV work in conjunction with the wiring impedance to limit the surge to an acceptable level. I would think that a Gas Discharge device at the service entrance, a big MOV device at the breaker to the stereo, and a surge protector at the outlet would provide a level of saftey from transients.
Chris