I agree with you insofar as the influence streamers (without DACs) have on SQ is concerned. So long as their output is bit perfect and you have a competently designed DAC, streamers do not influence SQ; as you say, their output is identical! But, I do understand why people choose to pay more and move on from a RPi or similar. I have used a RPi as a streamer and it worked fine but the available UIs (Volumio and the like) are or were somewhat limiting and the the machine would fall over every so often, or simply become inaccessible. OK, being a bit go a geek, I could always find it again via a browser interface, but you can imagine how well it went down with the family when they couldn't access their music and I told them to start by entering the Pi's IP address into the browser on their phones!
I think that it is worth paying a little more for usability and a decent UI, or even significantly more if you want a pretty box. Currently I use Auralic Aries Minis in two systems because they are reliable and I like the UI (almost as good as Roon, but free). These were not expensive (about £400) but unfortunately are no longer made. I get the impression that Auralic dropped them because customers realised that they were just as good as the full sized Aries devices, but at a third of the price! If one of my Minis failed, I think that I would buy one of the full sized Aries boxes, not expecting any change in SQ, but to maintain the UI because I like it.
Edit, I forgot to mention that I use the Aries Minis with separate DACs connected by USB.