I absolutely love push-your-luck games, but I think the underlying problem with this one is that the punishment for pushing your luck too far just doesn't feel like a punishment. I can spam the reroll button until I have a couple of crystals at a high value and then sell them. An idea, if you continue to work on this game, would be to charge the player money for each crystal that spawns in (except for the emerald so that you don't ever end up completely stuck at $0) and allow the player the ability to choose which crystals you want to spawn in next, maybe you want to go with some less risk lower value crystals or try for some higher value crystals and get a ton of money in return. And then make the return rate on the board (beginning: losing money, middle: breaking even, end: gaining money).
Overall though I think you had a fantastic idea, and the pixel art was really nice!