How do you know what you're missing?

Listen to unamplified live music. 

You said it - vinyl. That will open up a whole new world.

Here is the problem:
An audiogon post is about a general topic,
or a request for information, or even a direction.
People respond with what is working for them,
usually a favorite or new piece of gear.
The responses are particular recommendations,
usually.

This can send the poster on a merry go round of
options, taking twists and turns to an unkown
destination.

In a quandry over "where to begin," the poster either
may or may not try something new.  But then, how can they have
the reassurance that they are following a path that
will actually lead to better sound?  You have to be familiar
with how music sounds, with what you like, with different listening experiences (good and bad), I believe.

Some typical responses can be, "I like what this guy is saying."
"What if I follow THIS suggestion, maybe this will work?"

"I've isolated myself for many years, prior to current
circumstances."  From your 10/3 post, it looks like there
is a proposed trail of dollars, waiting to be spent.

I prefer to play with the tools that I already have, and keep
the change (no pun intended).  My quest is trying to make sure I am ringing the last bit of musical enjoyment from what I already own.
Under these conditions, a new piece CAN be justified because
I have "paid my dues," and my investment of  time, energy,
and dedication to the pursuit of better sound, is rewarded,
more times than not..

I hope your way works for you.

Read the graphs (frequency response, waterfalls, polars). Then compare them to other speakers.

In today’s market, where it’s almost impossible to hear speakers, much less in a good environment, I wouldn’t buy a critical-listening speaker if I couldn’t see the graphs, or that weren’t recommended by a speaker designer that approaches design from this technical perspective (planars and omni-directionals excluded). Subjective reviews are completely useless to me.

Cat, the sound of any system is a moving target but it does come down to what you hear. Imaging and sound stage are easy to qualify, tonal balance is not. Without a "calibrated" reference it is impossible to know what you are listening to. It is not at all uncommon to see people prefer systems that are way out of whack. A good example is if I increase a systems treble 3 to 6 db over 4 kHz many if not most audiophiles will think this is better. Distortion over a certain percentage is rather obvious and dysphoric. 
This is where good headphones come in. If you are not sure where you are listen back and forth between your headphones and the system. Ideally the tonal balance should be the same at the listening position. 
Describe what you hear as an image in a diary with three program sources that you know inside out. 
Listen to as many systems as you can. The best systems will float an image in space giving you a sense of three dimensions most systems will only give you two dimensions. 
Having said all this, your system is your system and if you prefer it a certain way that is your prerogative.
Others have mentioned comparing a system with live acoustic instruments. How are you going to play live acoustic instruments through your system? Those instruments are going to be affected by the room they are playing in, a situation you have no way of replicating.  
Good systems are always an evolutionary process. So you listen to as many systems as you can. Keeping a diary of your experience is always helpful. The system you liked the best is the one you start to emulate.