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

Which system?

It is hard to mentally compare now to many years ago, and while improvements each may have made significant changes in sound, they don't covey overall level changes of the type the OP asked about.
My best memory of what really significant change  has come about occurred when I was playing with my sister's college Thorens tt--a 145? I think with the original cartridge installed.  I listened to a few songs and was thinking of how this really sounded pretty good, and then I switched back to my SME setup and the change was almost startling.
 So I think that maybe inserting one component in your chain that is entry-level might be  a good way to demonstrate the differences that have been achieved in the evolution of a system.

Bill

So actually....
  I have 3 systems in my house.  2 of them are Surround Sound systems tha I regard as mid fi.  I didn’t start off planning to have two Surround Sound systems, but for a few years I had adult children living in my basement on a rotating basis and I cobbled together a system down there for their entertainment, hoping to keep them down there and out of my hair.  It’s been a few years now since we’ve had extended stays...
  My two channel system in a relatively small bedroom upstairs is my high end system, although judging by the standards of some here it would be considered mid Fi.  Speakers are B&W 803 D (the first with Diamond Tweeters, from roughly 2004).  Current Pre Amp and Power Amp are both Parasound Halo, John Curl.
I have 2 DACs—a first generation Mytek Manhatten and Bryston BDA-3.  3 Digital sources—Sony 5400 ES CD/SACD player, Oppo 203, and Bluesound Vault2.  Another digital source is my MacAir with Audirvana +.  I have a Synology NAS which I currently control with either the Bluesound or the Oppo.  I sold off my Vinyl Rig a year and a half ago, but it’s latest iteration was a Clearaudio Concept turntable and mc Concept cartridge with a Musical Surroundings phono Pre amp.
  I am not sure that you would care about the two Surround Systems, but here goes,minus the monitors.  My living room has a 10 year old Onkyo receiver.  Digital sources are an Oppo 105 which is also the DAC for the Bluesound Node2 and the latest generation Apple TV.  Speakers are Silverline Minuets as fronts , a Silverline center speaker, (these used to be rears until my wife got tired of every room in the house looking like a AV emporium) crossing over to a Paradigm sub at 80; rears are in Wall Paradigms..  The room for this system is fantastic, a perfect shoebox rectangle, and the only reason that it doesn’t house my 2 channel is that my wife spends a fair amount of time here (her space-she watches a bit more TV than I do, sits here with friends, etc).  And although the equipment is more prosaic here, I’m always impressed and just how good this system sounds when I have the house to myself and get to experiment.
  Basement surround: Speaker fronts are Silver Panatellas (long discontinued floor-standers), Center is aBoston Acoustics, and so are the rears.  Pioneer Elite Pre Amp outputting to Parasound 5 channel power amp, and a Pioneer Elite DVD/SACD Player connected to the Pioneer receiver by “I Link”.  A cheap Sony BDP, another ATV and Bluesound Node2.  This system has to compete with my Forced Air furnace which is one noisy sucker, so that and potential flooding concerns exclude this from ever being the main listening area.

Good response noromance, real good.