I would argue that NVS, which does indeed work on an identical principle to the headphones, reduces the damaging effects of vibration stress on the airframe because the the 'mirror' vibrations created by the dampers cancel out the original ones from the engines and props.
Think about it this way:
Listening to headphones loud harms your hearing. If your anticipated outcome re. NVS is true then we would predict noise cancelling headphones caused even more harm. This is not the case at all - the overall result is significantly reduced noise NOT more noise added and as a result of eliminating the background you can reduce the chance of damaging your eardrums by setting your music to a lower volume.
As an aside, on a FlyBE Q400 trip from ABZ
a year or so ago the system must have been inoperative because the noise and vibration was staggering. I have always thought these birds are very pleasant on short hops around the UK - but this is certainly not so when NVS is off.
However A Q400 with NVS off is still much better than Logi's Saabs...
[Edited 2007-01-11 12:00:20]
[Edited 2007-01-11 12:01:26]