I have heard numerous times that the more powerful the amplifier, the better the sound will be even at low volumes.
Not a yes or no answer for that one, in my opinion.
For instance, Atma-Sphere builds several OTL amps, all similar designs.
The baby is 60 watts and two above it, 100 watts plus and one 200 watts plus. All three of these sound excellent and very similar at moderate volume levels.
In this case, the extra power of the larger models is not an advantage unless needed for sound pressure level or a more difficult to drive speaker.
On the other hand, my personal system was powered by amps from 40 watts to 750 watts and the various designs (read, different companies) did sound very different, even when using a fraction of their total output.
All amps have a personality and all speakers respond to the amp driving them. It's possible to love a speaker with one amp (low or high power) and not like it with another amp (low or high power).
Sorry to be confusing, but the point I'm making is power is important, design is important and matching is important and often an amp gets credit for the wrong reason.
A perfect example. A good friend in my group owned VTL 750's, just as I do. He powered his Kharma Exquisite speakers with them and on a lark, tried a par of the Lamm SET's. After a week, he sold the VTL's and kept the Lamm's.
The Lamm have only 18 watts per channel and the VTL's have 750 watts per channel. The VTL sound is dark, dynamic and contrasty and my friends room is VERY damped acoustically and his speakers sounded more lively and transparent with the Lamm.
Obviously in this case the personality of the Lamm was more appealing than the superior power. Both these amps are very high quality and both are expensive.