Your impressions match mine of your recordings. I agree that it is subtle to the point that we're going to be the only ones who notice enough to care, especially in a live situation, maybe the differences would be better appreciated in a studio environment.
I've done my own testing on this. I've been using wooden dowels for years now and they have definitely helped my bass. When I started I was very skeptical and really didn't want it to be true, because they aren't as strong as metal and they don't have notches to lock in, like your metal pin does. I will note that I'm using wooden dowels, which is different than what you have there, which appears to be a metal endpin inserted into a wooden endpin. I haven't tried that.
I have also tried different woods; maple, oak, mahogany...and they all sound different. I walked out once and when I came back, Jake was playing my bass, but had switched woods and I could hear it coming up the stairs. No doubt in my mind, but is the drummer who I play with going to notice? He might think that things are better or worse tonight than some other night, but the endpin would never make more difference than the room or the stage.
I also concluded that if I was really dialing in, I might opt for difference choices if I switched strings. Maple would brighten up darker strings and mahogany would mellow out new Spirocores a bit, but then it just becomes a question of how far you want to take things.
For me, I'm happier with wood than I am with metal, or at least the metal endpin that I have. I have no doubt that a different metal endpin assembly would produce a different sound too.
Thanks for doing this, I enjoyed hearing you play as well!