Damn, what else are you gonna spend those on Mr Scrooge?
Bungie has demonstrated that they love to add new uses for currencies so I am always anticipating something like that in the future.
I'll check the rolls because a lot of armour was upgraded via Xur and rarely was a better roll when upgrading. I hate that they made it like that.
I don't even bother with stat differentials unless it's beyond 25 or so. Otherwise the in-game change isn't pronounced enough to relevel gear.