This is a hot potato if ever there was one.. How much power? In simple terms, "as much as you need to reproduce the desired program material without audible or measurable distortion".
Loudspeaker efficiency plays a huge role, as does power compression and flux/core saturation in dynamic drivers.
Most any high powered audiophile system is going to be fine with Chamber music. Things get a bit dicey when the program consists of a full orchestra with big bass drums. Even more interesting when there's pipe organ and 32' pedals, on top of bass drums. Still more interesting when it's the 1812 and there's live cannons in the recording!
I've been through more than ten iterations of stereo systems since the 1960s, pursuing my goal of unfettered audio performance. I've moved from my OTL triode amps to solid state and went back to tubes for a while until the SS got better. I remember my first SS amp, a Fisher TX200. Ugh. Awful sound, unreliable and unstable.
In search of decibels, I built many horn-loaded systems, and used molded horns for midrange. That was the tail end of the tube era for me. They were pretty loud, but sounded awful.
I continued going up in wattage, to 800 wpc with the Phase Linear D500, but the speakers of that era just kept smoking and failing. Not to mention microscopic amounts of Xmax on so-called "woofers" of that era, all combined for a frustrating experience and many trips to the reconing shops.
Things got better in 2006, and new woofers were finally able to reach parity and beyond with the very fine mid/hf systems I was using since 1982. The wattage went up even more, and multiple arrays of speakers increased overall efficiency again through mutual coupling.
A while back, I did want to get some hard data, so I ran a 2.0v rms (measured with H/P AC voltmeter) brown noise (band limited 0-150Hz) into one dual 18" woofer cabinet (4 ohms) and measured the SPL, which was averaged to about 112dB. With the whole array of speakers operating, a 'signal present' threshold on the QSC amplifiers is 6 watts per amplifier. From the listening position some 8-9' away, the SPL runs about 129dB. When the -20dB LED starts to flicker, SPL hits the 140dB range, the meter's limit. But that's loud enough for me.
I run 2000W into each mid/hf driver (2000W is the short term measured dynamic head room into 8 ohms) which are industrial/professional drivers of very high sensitivity, have 4" voice coils, only .4mH of inductance and enormous power handling.
I listen to a lot of interesting stuff, mostly recordings I've made of pyrotechnics, orchestras and other stuff. Fireworks require very fast transient response and the ability to go very loud (close range recording, in this case, I was commissioned by Zambelli Fireworks to make a sound and video recording of one of their shows). There are probably only a handful of sound systems in the world that can reproduce the transients and the SPLs realistically.
Telarc's "1812" used to be a benchmark, though I was aware early on that at least 5 of the cannon shots were badly clipped in the recording.
My GBS recording sessions demonstrated that the loudest orchestral peak was 105dB at 4th row center, during rehearsal with the full orchestra. Average levels were around 97dB for all but the very loudest crescendos involving percussion.
At home, when I'm listening to Classical, I use the 105dB max peak as reference level. But when I listen to pop/rock or some heavy electronic music, realism becomes an oxymoron due to the electronic nature of the music--it's not acoustic anymore, so the rules about calibrated SPL are out the window. So it's 'as loud as it feels good' and for me that usually ends up with bass at around 137dB, enough for solid full body vibration, but not so much as to prevent breathing.
So, how much power? That depends on what you listen to. I currently maintain 16.5K of amplifier power on tap, though the circuit breakers would never support using anywhere near that amount. But I haven't blown anymore speakers since the 2006 upgrade.
. There is absolutely no issue with sharing experiences and opinions of audio. You can say that black is white and white is black as a matter of *your opinion* and that is OK. 
