The web can have a new feature like loot box, when opened up they could give you some points which you'd later redeem as a boost of your own choosing for let's say 10-50% on any category in earning. Also boosts could vary in the amount of time with given % on the category.

The loot box could also have rewards as the main currency. Maybe even EXP for the account? Though then levels on the account should be also rewarding. I think that the boosts should have and off and on switch, to let the user decide when they want to use it, that would be the best. And the reward for the currency could come as a random generated coupon code, that way it would be shareable as well.