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

This hobby should be about finding the system that provides you with the upmost musical experience, not what others, whether they are professional reviewers, hobbyists, or friends, think or say. Too often this hobby is not.  So do not create stress for yourself regardless of whether others tell you they can or cannot discern differences between streamers.  It appears you have been diligent, exploring a number of excellent component streamers and reaching a conclusion on the one that satisfies you.  The fact that your choice is a lower cost option, or is published as not best in class, is not significant.  What is significant is that it blows your hair back.  Be happy.  My recommendation is to use the savings to immerse yourself live musical performances and listen to the real “absolute sound”.

Only last week, at a friend’s house we did a comparison between the streamer of a Hegel H590 vs a WiiM Pro Plus streamer. The WiiM was fed into to the Hegel via Optical and Coax at different points. The DAC used for all three instances was the Hegel’s. 
We also requested his wife- who likes to listen to music but is not fussed about the equipment at all- to give her opinion as to what sounded “better” to her. She couldn’t see which component was being used- not in her line of sight.

All three of us voted the WiiM as easily besting the Hegel’s streamer. We were very surprised. On coming back home (to Dubai, from NY where this took place), I bought a WiiM Pro Plus.

In my experience it’s all about system dependency. Personally I have found a significant positive difference with Aurender N20 and Grimm. Several others didn’t make an impact to justify the additional price vs my NUC i7. Even if the Aurender and Grimm made a significant difference, I didn’t feel that being big enough and decided to stay with NUC and rather add a Farad 3 with Shunyata power cable. I’m happy this way and I don’t feel the need to add another expensive box. 

You’re not crazy.  The sonic differences in upgrades become more subtle once you have high quality components in my experience.  I have moved from integrated components to separates over the years.  The biggest differences were in the speakers, DACs, streamers, and CD players.  The source and end point components.  Less with amps and preamps in my experience.  I moved from a Blusound Node N130 as a streamer to an Innuos Zen Mk3.  I noticed a difference.  Beyond a quieter background I found it stayed connected to my wi-fi better.  I use a cable from my router directly into the unit.  I have my equipment setup in such a way that I can A/B test when I try new components.  If I don’t hear a noticeable difference I return the new and more expensive gear as you did.  Trust your ears.  

I think one should just be happy with whatever sounds good. It doesn’t matter if one has a $500 streamer or $5000 streamer. And that applies to speakers and other equipment. Enjoy the music and you are not crazy.