Good to see you've thought up some of these points already. For me, a complete reset is the best - in terms of player statistics or in-game boosts. Once a player knows how to game the system, they can easily reach the level required to use their old powered up items, and then the playing field is gone. What you could reward returning players with instead are boosts to exchange rates when they do cash out crypto rewards.

Another thing this brought up: don't allow people to buy ridiculously powered items/stats/boosts. Again I will bring up Utopia, where you could pay to remove ads, but nothing you could buy would improve your edge over other players. This is the killer in the end.