High end stereo preamps? Worth it?

What makes them worth it? What  qualities, preferably not expressed in purely subjective terms, makes a high end preamp that?
If I were to observe that a well designed $300 DIY preamp was indistinguishable in group blind testing from a Halcro DM10, and actually measured better, what would your response be?

If you're into DIY you can build a preamp pretty cheaply that matches, and in some ways exceeds, the specs of any of the high end preamps, and has a sterling reputation for audio quality.
https://audiokarma.org/forums/index.php?threads/high-gain-opamp-based-preamp-for-low-output-mc-cartr...