I'm incredibly jealous. I've made over a million gil NPCing Waltz Shoes without seeing more than 2% Waltz potency. MP/Acc/HP/Light are in one augment slot that occurs 100% of the time and Waltz potency is alone in a second slot that occurs about 10% of a time. High values are much less common than low values, too. You got lucky, sir! Hats off!
I haven't seen another pair like these, but not many people walk around in their waltz gear (I did for about a month after this). I feel like an *** for saying it was only my 2nd or 3rd attempt :x