he stores them all in a massive vault and swims in them like scrooge mcduck. you would not believe the tingling sensation that gives you from all those warm and gently vibrating coins surrounding every inch of your naked body.
I'd reckon he uses them to buy his momma a super expensive, all access pass at the local salon so she can relax and have her face-tentacles massaged :P
Strip club.
It's the future so the strippers are all Fallen, Hive, and Cabal. They send the coins to their loved ones who maintain the keepsakes on their person when the guardians invade their homelands. That's why engrams always decode into them. We take them back to Xur to purchase his crap and then the whole cycle repeats.
It's also why Xur only appears on the Weekends.
You see, in the future, strip clubs are only open Sunday through Thursday and Fridays and Saturdays are when people work.
Oh shit!!
What if the Nine have a break room with a kick ass vending machine and Xur needs some extra money to afford all his snacks.
He takes out the trash (Exotics) because -blam!- that noise The Nine don't need no Exotics.
[b]Not when they have their Secret Mythic Pearlescent gear. [/b]
He thinks to himself
[b]"I bet those dumbasses at the tower will give me so much money for this crap" [/b]
and BAM Xur spends his days off on the tower making that munchy moolah
We have made Xur rich in snacks and we are driving him toward obesity. We should all be ashamed of ourselves.