Too Much Power

Aside from greater potential to blow up speakers accidentally, excess power in-and-of-itself is not a problem.  But, in the real world, how one gets there—running many output devices in parallel— could reduce sound quality.  Many years ago, I heard a demonstration of two Rowland amps that were very similar in build, one rated at 50 watts, the other something like 200 watts, running power hungry Magneplanar speakers; I preferred the 50 watt amp, particularly at lower volume levels where the big boys sounded lifeless.  One manufacturer of high end gear touted how his amp used only two output transistors per channel, that is, until market demand compelled him to make an ultra high-powered amp.

I run high efficiency speakers, and with my speakers, the very best sound I’ve heard comes from low-powered tube amps.  One of my amps is an Audio Note Kageki (parallel SET 2a3 rated at 6.5 watts/channel), the other (my favorite) is a custom-built pushpull amp running 349 output tubes (5.5 watts/channel).  I also liked, in my setup, a First Watt J-2 solid state amp that is low powered.  Perhaps I do compromise sound at higher volume levels, but I rarely play my system at high volume levels, and even when I do do, the average output would still be below one watt, and I choose not to compromise that watt with amplifiers that don’t sound as good.

I believe the answer is it all depends. Btw, the answer that a "too powerful amp" endangers the loudspeakers posted above is completely false. I would even go so far as to say that an insufficiently powerful amp is more dangerous to loudspeakers than a "too powerful" amp simply due to distortion being potentially harmful when an amp is overdriven. But why does it all depend? Because different amp topologies behave differently with different speaker loads. In general the answer is "no". While not directly responsive to the question asked, also consider that with most amp designs, more power means more output stages. Some of us believe that less output stages result in purer sound. 

Why is there the oft-dispensed advice to choose speakers first and then the amp? Because if the loudspeaker is easy to drive it may be best to choose an amp that is not overkill in terms of power for that particular loudspeaker. That said, there are other factors that go into choosing an amp for any given loudspeaker. Some of these criteria are just empirical experience as to what mates well in terms of system synergy. That said, when JA of 'Phile measures an amp and concludes that it needs to be mated with loudspeakers of a certain impedance of vice-versa, that advice imho can be relied upon. 

Plus one @fsonicsmith 

As we say in hotrodding, too much horsepower is almost enough.

@gnoworyta I'm nowhere near an expert at this type of thing as well or in the different classes of amplifiers but I do own the M1200 and EXTREMELY pleased with the SQ and price performance

In the reviews I read prior to purchase the references to the power rating reveled not in how loud the amplifier could play, but the ability to create a larger and deeper sound stage with headroom remaining to deliver the sonic peaks with equal performance

Rest assured the M1200 delivers as advertised, IMO

I've paired the M1200 with speakers rated at 900 watts and have little concern about over powering or damaging them

The symmetry between the M1200 and the speakers is a thing of beauty, again IMO

It's two channel with no subs and do not feel I'm lacking in bass performance.  Though truth be told that's one of the areas that you don't know what you're missing until you've heard it, sort of things.  I'm not ambitious enough to go through the brain damage or cost get my room equipped for 3 or 4 subs to do it justice

Relative to volume, on a scale of 1-100, I typically begin playback at 35, the sweet spot for most recordings is 45-50, hi-res formats come alive between 50-65, and rarely if ever have turned the volume up past 65

I begin to get wide eyes and big smiles from guests around 45-50 and reactions of WOW in the 50-55 range

Here's a review from TAS that sums it up more technically than I ever could and if I'm not mistaken in 2021, the M1200 was also on the editors choice products of the year list in TAS as well