What improvements did you hear in going from entry level to high end Audio?

More body and detail.louder without any distortion.Natural timbre. Big improvement in bass. Uniform across frequency range. 

A better audio system allows me to hear with greater detail and resolution, the faint sound of money draining from my bank account!

My first venture into home audio was back in the mid 70s. Quite a basic Lo-Fi system consisting of a Fisher receiver with a pr. of BIC Venturi speakers and a Pioneer TT.
A few years later, while on a road trip, I happened by a Stereo shop and decided to step in. WOW! Large beautiful speakers, the likes I had never seen - Klipch Corner Horns, huge Altec speakers, tall ultra thin speakers they called Magnapans and a whole host of smaller speakers - Thiel, Spendor and others. In addition to speakers, they also had racks of interesting amplifiers and players. After some hours of listening to a variety of systems, I came to appreciate that an audio system actually could sound allot like a real performance in my home.
My current taste in music is broad, but since my preference is for anything with good vocals and live, real instruments - I lean towards electrostats, ribbons and open baffle speakers and somewhat prefer tubes.
Cold, dark and revealing (regardless of how pricey) doesn’t work for me, If it lacks the body, richness, air and harmonics of live music.
My current system (well south of $100K) even though there are some things I’d like to upgrade, along with being quite detailed, manages to click most of these buttons (body, richness, air and harmonics) for me.....Jim

When I went from a juvenile all-in-one TT/radio/speakers to a 25 watt Kenwood receiver, Dual 1218 with a Shue cartridge, and some neat little speakers a friend gave me (don't know what they are, but they still play after 45 years) the main thing I was looking for was LOUD without distortion. When I moved to a Nakamichi Receiver 2/ Stax SRD 40/ Yamaha YP B4/ Shure V15 III I got "realism" and crystalline clarity. Those headphones let me hear thinks I never heard before and I could understand lyrics a hell of a lot better. Then I added a pair of Boston Acoustics T-830s and I got a room full of performers, not all piled up on each other or the same depth.

The system I have now includes, first and foremost, a room that lets me position myself and my speakers properly. I waited a very, very long time for that! The rest of the system cost me about $8,000 over the years. It would be twice that if I bought everything new today. Now I define realism differently, I can hear micro detail (would that my listening equipment was still as good as it was way back) and space is 3 dimensional, independent of the speakers and the stage extends wider than their placement. I can count the number of back-up vocalists and usually identify them. (another of my avocations) I believe my humble system now exceeds my ability to hear, as cable upgrades no longer provide any audible improvement. I enjoy the finer LPs, SACDs, DVD-As, etc; but the music is what counts. Thank goodness there are so many fresh new artists creating unique new music, such as Nicole Atkins, Eileen Rose, Chris Robley, Frazzy Ford to discover and some oldies that I passed over, like Gene Clark, Patsy Cline, Joan Osborne, and Emmylou Harris. I still obsess over the lyrics and try to get what the writer was thinking, Just like I did when I thought Neil Young's Hello Mr. Soul was about a friend turning him in for drugs (wrong) or Peter Gabriel's Red Rain was about Jonestown (wrong).

Don't tell my wife, but I've spent more on media than equipment.

Amongst others, dynamics are important to me, and the upgrades I have bought over the years are getting me closer to life performances. As we all know, it is never difficult to tell the difference between life and reproduced sound, so my objective is to get as close as possible to the life sound of (acoustical) instruments.