Maybe reward players for having Credits stored up in either their wallet or in a new Bank building.

There could be a fixed interest rate (devs can determine a fair/balanced value), but there could also be a new Crew Class (Financer?) to improve the interest rate. There could even be a cap to the amount of Gems awarded this way per day.

This would help generate more Gems for players (the current progression bottleneck) while incentivizing players to actually haul all those Crystals back to the Market (instead of just leaving them on the ground and moving on to the next mine)!