Discerning a difference between streamers is difficult...only me or common for all?

OP - I, too, was prepared to climb the upgrade ladder on streamers but have creased, at least for the time being.  I went from a Bluesound Node 2i using its DAC, to using the Node 2i as a streamer but a Cambridge CXA81 DAC, to a miniDSP SHD streamer/DAC, then back to a Bluesound Node 130 with a LPS into a modded Peachtree Gan1 power DAC.  Now I have implemented the Bacch4Mac and Bacch ORC system; I simply use the Qobuz app on the Bacch's Mac mini fed into an RME interface and then to the Gan1.  All along the streamer is fed by Ethernet via an English 8 switch.  To be sure, I haven't compared SQ with any of these configurations to one with a high-end streamer like Aurender or Innuous.  For me, so far at least, the big gains in SQ were in the DAC, the Bacch processing system and the power amps, definitely not the streamers.  In fact, what I found was that the big difference in streamers came from their user interfaces, not SQ.   I really enjoy the music now and have no desire to upgrade anything.  Best of luck.

I'm not sure my experience will be all that helpful but here goes. I have three Auralic streamers in three different systems: an Aries Mini plus S-Booster LPS, an original Altair, and an Altair G2.1. These were purchased over the course of some seven years, with the G2.1 arriving a month ago. (Auralic was blowing them out at nearly 60% off, no tax or shipping, to make room for the G2.2, and I couldn't resist.) I only stream Tidal, not files. In  my main system I listen almost exclusively to vinyl (two turntables, four tonearms, three phono stages). Each step up the Auralic line has yielded obvious improvements in SQ. Stark, not subtle. Just to be sure, I compared them in my main system. So IME, at least with offerings from a single manufacturer, the differences are clear. Whether differences would be audible between manufacturers at the same level of component I do not know. I will say the G2.1 sounds remarkably good, even next to my high-end vinyl rigs.

I used to be a big doubter that there could possibly be any difference that you are actually hearing rather than just perceiving due to expectations, subconscious or otherwise. I now am convinced due to first hand experience that things can get weird and go wrong in all sorts of unexpected ways. Technically nothing should be perceptually changing, but that assumes everything is working correctly. Some faults are so obvious nobody would deny it if they heard them. For instance, if I use Apple Music to stream from their service, every song has a short stutter near the start of the song. This is a well known issue that Apple doesn’t seem to be able to fix, and it isn’t the same for everybody. Somewhere there’s a complex wrench in the works. Something ain’t right, and it makes you wonder what else ain’t right that might be more subtle and intermittent, thus not always showing up on single measurement tests. If I rip my own discs and don’t stream, it never stutters. Other streaming services never stutter.

I’ve got a device that runs optical audio in to my computer via a USB converter. It is unstable, and sometimes it does really weird things. If it gets bad enough, the music just stops.

On my Blu-Ray player I sometimes get audible and visible static. Just touching the HDMI cable will usually stop it for a while. Bits is bits, but they don’t always show up at the right time.

So, maybe you’re not hearing much because there wasn’t much going wrong in your particular system in the first place. I’m assuming here that in many lower end systems, like mine, many subtle things might be going wrong that happen to much less of a degree on better systems like yours, especially if you happen to have good synergy between your components, even if they aren’t at the very highest class levels available.

Although I've posted this before, this is an apt thread for it. I don't really stream except playing my downloads from my computer and Apple Music on the computer. I have an ifi pro idsd dac I got used and added an Iris DDC (though I'm selling the Iris to upgrade to a Hermes). 

I got a T+A Dac 200 in trade for an integrated amp I was trying to sell and then added the Aurender N200 streamer after reading all the comments about how good streamers and the Aurender were. 

I was able to set up both systems to quickly A/B them because I agree and know that audio memory is very short. So I could almost immediately switch between the 2 systems. 

The Aurender/T+A set up had slightly a slightly larger soundstage and a bit of a digital glare. This is a system that was essentially $12k more expensive than my usual system. I switched back and forth numerous times and could barely hear any differences other than what was mentioned above. I sold both the Aurender and the T+A taking a bit of a bath but regaining most of my ill-spent funds. 

The Iris DDC added much more to my system than the Aurender or T+A. I am going to try out a PS Audio Directstream Mk1 that has been slightly upgraded to see if it is better than the ifi plus I can try an I2s connection to see if that is significant. The Iris had to go only because it's I2s connection is not compatible with the Directstream thus the reason for the Hermes which can adjust the pin setting and the Iris can't. 

So right now, you can say I am a streamer skeptic. Plus I didn't hear any added benefits with using Qobuz or Tidal which I did a trial of each. 

I took a less financially “lossy” route. 
I found a used Lumin D2, and have been quite happy since.