"unused is just that, unused".
to this i would say: how do you know it will be unused all the time?
even if it's used rarely, it would prevent you from getting distorted sound or compression or unnaturalness.
this is the very reason i updated my audio system; once in a while, i did not have quite enough power; the distortion was bad, there was compression, danger of blowing tweeters, and low-fi sound.
now i got M80's that can take the power without distortion, and enough power that i will always have some spare, thus, no distortion, clean sound at any level.
i always listen to movies at reference level and to music at realistic level. only the dishes in the cupboard produce distortion once in a while, but i don't hear it, it's overwhelmed by the speakers sound level.
don't forget that not enough power is more dangerous to speakers than too much power.
take a 50 watt amp and use it at maximum volume in speakers rated at double or triple that many watts, and you'll get speakers that smoke.
