When a reference is made to wabi, it is usually made with respect to the external aspects of a watch - a dinged-up body, scratched crystal, a repair and so forth. The word itself derives from the Japanese phrase wabi-sabi, see Wikipedia here.
Wabi . . . . . can also refer to quirks and anomalies arising from the process of construction, which add uniqueness and elegance to the object. Sabi is beauty or serenity that comes with age, when the life of the object and its impermanence are evidenced in it's patina and wear, or in any visible repairs.
Which brings me to lume on old watches. Here, utility conflicts directly with sabi, because most old lume doesn't glow much, if at all. Radium itself lasts a long, long time, but it's radiation does kill the phosphor in most paints of the era. Promethium barely lasts a couple of years. Tritium lasts longer but is still getting quite faint after 20+ years. Now some people want their lume to glow, whatever the age of the watch, and often have their watches re-lumed with modern stuff like SuperLuminova - while others consider that to be heretical. Here's a couple of 80 year-old watches that illustrate the difference:
At left is a re-lume using what looks like Luminova, color code C3 green. At right is the same model with it's original lume, a sort of faded mustard color.
Both have wabi, the lume having been applied by hand. At left, there is also a little sabi because a re-lume is, after all, a repair. At right, sabi positively abounds, IMHO: the fading of the lume color, the pieces of lume missing from the hands, the different hue of the lume on the hands.
I prefer the one on the right, which is a good thing because it's from my collection ;-)