Is Louder always Better?

i'm inclined to say yes.

first, context: you are not generating impedance mismatches when A/Bing gear, you have amps w/ more than enough power for your speakers / room (ie no clipping) and you haven't disconnected your tweeters (ala monster subs in cars) or sitting horribly off-axis.

the thing about home audio (digital particularly) is that as external noise is reduced, you are left w/ a purer signal--simple S/N ratio folks. generally, live instruments don't hurt your ears, but when a home rig does, i'd contend that its the noise riding on the signal, as its mostly concentrated on the upper mids thru treble, and this is where fatigue is generated (again, monster sub in car example for bass as non-fatiguing). the external & objectionable noise found in this frequency range determines final listening SPLs (the listener naturally arrives at a volume setting where the artifact noise doesn't cause overt fatigue). as noise is reduced, the final SPL level can be increased while generating no incremental listening fatigue.

but, at all volumes, it also implies greater microdetail & clarity (again higher S/N ratio), while also being more enjoyable---i consider those findings as evidence that 'louder is better' is a fine litmus test. if you make changes that result in your listening louder without your ears immediately objecting, you are highly likely listening to an improvement in home playback (given original context).

what is this getting at? external noise (aka Distortion) not only obscures micro-detail in the upper mids & treble, but it also causes listening fatigue and ultimately limits the volume you can listen comfortably at (ergo the thread title). i've found that external noise removal is a function of 3 efforts, all of which are equally important:
1) power conditioning
2) vibrations
3) room acoustics

(one visionary poster referred to them as the holy trinity of audio, i agree).

i figure i've put 10% of my audio budget into these 3, and it ultimately is the difference between a decent but disappointing rig, and a very satisfying one.

YMMV, but probably won't.