Hi,
I'm no expert at fired enamelling; I have studied the various aspects of high watching, as an academic (as opposed to a practitioner) and as a collector, for more than a few years. And I tried to do so without blinding brand or industry fanaticism. Dials and their techniques are one aspect of this...(previous to put into context my comments following)
Look for evenness of the surface
Look for smoothness of the surface
Look for vividness and correctness of the colors, and how well separated they are, and how well blended they are, where they are supposed to be. If they are supposed to be well delineated, then they should be well delineated and not "bleed." If they are supposed to blend, then they should blend naturally and beautifully.
Look for pitting, which usually indicates that bubbles occurred in the process which were not properly addressed (by limiting the number and severity of bubbling during the firing process, and by sanding and resurfacing and then relayering and refiring, over and over again until the resulting surface is as smooth and free of pitting as humanly possible)
Look for fading if the dial has aged.
Look for the aesthetic quality of the pattern presented.
These are the most basic and obvious touchstones for a collector/hobbyist to evaluate a fired enamel dial.
Yes, true high grade fired enamel work is very rare, both in terms of companies doing it, and qualified, experienced practitioners.
Cheers,
TM