The other interesting thing is that less clock jitter is not necessarily perceived as better.
That seems to be true, at least to some people in some tests...I've probably read same things about this as you.
I'm not ever selling my modified things or updated whatever, those have been purely for my education and fun, as you said. However, there have been some instances where other people have asked if I'd do the same thing into their gear, after hearing my stuff. That's a little bit different situation, and I have modded couple of things like that, no money involved.
Even though I understand the need for common reference points and proof, I'm not a big believer in "highly scientific" AB tests myself. I have listened some of my gear, the very same gear, even for decades. I will know instantly if something is not the same, given that I'm fully aware of my current state otherwise too and can adapt. The amount of rest, physical and mental stress levels, emotional state, surroundings with all the variables, they all have impact in how we hear also....or process what we are hearing. Being tossed into situation where many of the variables are not familiar and then presented with gear you have never heard before, and having no control over the music used, volume levels, nothing...man, I can hear pigs singing in tune or then again, might not even tell a mp3 from SACD. That in itself
might be telling something about the lowest common nominators, but not necessarily anything about the best I can strive for by myself. Can't necessarily prove anything, don't need to prove anything.
All this is of course different for people who would need the proof to sell something.
Fun stuff to talk about, but maybe enough for our forum here. Rest assured, my system doesn't have wooden volume knobs and the cables are not floating above the floor level, neither do I listen frozen cds or use exotic (snake) oil...but I can't really diss some people having that fun with their gear either.
Bringing this back to the original question, even a working mod might be useless or even worse than the original, if not applied well. I've seen some well made clock circuits myself, hacked into players in a way which will bring some troubles. For all that I know about that stuff, that is. Might not be much, after all. Also, a working improvement in itself and applied well enough, might still make the whole sound worse. Now the better part is just revealing a problem somewhere else that was hidden before. Some things are better left alone, otherwise you'll end up building the whole darn thing anew...done that too.