IDK man. I got three Antiquated Runes from my last 3 nightfalls (pre-update). 31 Three of Coins is worth 3-5 exotics. Granted, it is a pain in the ass and a lot more work to use them all, especially in a week. Exotic drops should be at least a 33 percent chance every nightfall. That way you would be almost guaranteed one exotic between three characters each week on the nightfall.