One facet not touched on is what is 'adequate' for the listener. I literally did not listen to much music for about 15 years, despite having a 'decent' stereo. One day the wife asked why, and after some thought I replied because it really did not sound much like music to me.
Fast forward about 3 years - I listen to music every day and look forward to it. I spent the time changing my system to components that sounded like music to me. All equipment was used, often obscure, only a few pricey bits, and the amp and speakers built by me.
It was a real experience to listen to the system in progress, try to determine what the problems were that were nagging at the back of my mind, and figure out what was at fault and how to resolve it. Everything got touched, and there were a number of real revelations.
Money may help you get a good system, but it certainly won't guarantee one. I went to a local high end hi-fi shop during one of their events, and could not believe how bad their show systems sounded. Often it is flash rather than quality sound. It is the job of the listener to assess that one, and money won't help.