I feel any day now the Emperor is actually going to just gift me a flaming bag with a heretics turd in it because he is obviously having a laugh.
Sire Melk is clearly another big player in the heretic turd business as he tries to sell me several of them every single day.
These mystery boxes may as well just be weekly fruit machine pulls. I am yet to even come close to hitting the jackpot.
They should cut off one of Melks arms to make it obvious that he’s a one armed bandit… 
IMO, they should change melks mystery boxes into unlimited (small/easy) box contracts that you can take that don’t cost currency. When you complete them you get a mystery box.
They could also change the emperors gifts to always at least reward a grey weapon when they would have otherwise awarded nothing. Seems like it’d be easy enough to adjust the currency reward to figure in the discard value of a weapon from every mission.