@audphile1 , I suppose that to be honest I do fit into a couple of the categories on the list. Although, with all things being relative, my equipment is probably okay, my room is small and acoustically untreated and I am near-field listening (unobstructed equilateral triangle) which I have read on this site may take the room somewhat out of the equation. And I suppose that it is possible that I either lack the ability to hear all sonic changes or I may lack the ability to realize that I am hearing all the differences.
However I would say that: I did make a couple of equipment upgrades in the last four years (the SA10 that was kind of the driver for this thread and a SLP-05) and I was able to hear the differences, particularly with the SLP-05. Also I will say that I have been rolling some pairs of 6SN7s in the balanced input sockets of the SLP-05 and when I put a real nice pair in there, I definitely do hear it. Also, with good source material in the SA10, the sonic effect works magic on me. As an example, last night I played three discs that I liked the music on: the Sony SBM (redbook) remaster of Born To Run sounded like nails on a chalkboard, the MFSL redbook of Goodbye Yellow Brick Road sounded better on certain tracks but overall not a whole lot better, but when I put the MFSL/SACD of Cowboy Junkies Whites Off Earth Now . . . as I typed--magic. I wish my oldy but moldys could sound that good.
So with that last paragraph typed, I am not completely devoid of the ability to hear, and I’ll just have to see/hear how it goes. I’d also say that way way back in the days when I upgraded speaker wires and interconnects, I do not remember being slapped in the face with an "OMG, that sounds better!" but I do know that I felt a contentment when I was listening that drove me to listen longer and more frequently. Of course, I have no doubt that my hearing was better back then.