All other things (like size and number of speakers) being equal, the difference between a 50watt amp at maximum volume and a 100watt amp at maximum volume is 3dB.
So are 3dB worth the extra money? You tell me.
On the other hand, doubling the number of speakers at the same level of power will double the apparent volume.
More watts = impractical
more speakers = smart
Only pay for what you need.