Aside from a few zealots, I don't think anybody has an issue with developing greater things, pushing the boundaries, and so on, particularly for DIY designers. Hobbyists tend not to like what's just "good enough", and that is well and good.
However, I do think that there's a huge value in recognizing "good enough", particularly when giving recommendations to others. There's no underlying justification for $1000 headphones to be paired with $1000 amplifiers or DACs, yet that kind of thinking is prevalent. I mean, not everybody is a believer in the cost = quality metric, but it's too many people. To me, a lot of arguing at the minutiae can make us lose sense of the big picture, if the goal is to get good sound (which is not the only goal out there, which is fine). I'd ask questions like: "Do I need an amp with -110 dB distortion when my headphones have -70 dB 3rd harmonics in the midrange? Do I bother upgrading to something with even better performance?", "If my headphones probably have a dB or two difference in channel imbalance at many frequencies, is a 0.5 dB difference from a good potentiometer at the very low end of the rotation a huge deal?", and "How much should I worry about 'unmeasurable' amp parameters that nobody has yet to demonstrate, that supposedly have a significant contribution to sound quality?"
As for evaluating how "objectively" good some amps are, of course there's some room for interpretation of what parameter matters more, by how much, and so on. But hopefully, our conception of what matters is grounded in reality, based on previous research. For example, we know that X levels of certain kinds of distortion are generally undesirable, because people have tested for that before. We can also test ourselves to some extent, though most peoples' ideas of self-testing are often not that rigorous.
Ideally, part of the objective evaluation of amps and DACs involves rounding up a great many test subjects and having them take a listen and rate them, hopefully controlling for such things as expectation bias, order effects, and so on. Unfortunately, nobody has the time and resources for that.
Edited by mikeaj - 8/3/12 at 8:29pm