Fact 1 : I don't buy any random box, and now have 13000 CC piled from monthly fees since the beginning of F2P
Fact 2 : I might be enclined to spend some coins if some of the boxes' content were avaliable to direct purchase, even if it costs more than the actual boxes.
Box costs 450 CC, and contains multiple items.
A single "average" (silver symbol) item could be purchased directly for 600 CC
A single "rare" (gold symbol) item could be purchased directly for 900 CC.
Except that at their rarity, gold items would be sold for 3-5k CC, and then people probably wouldn't buy the boxes OR the items.