In case you are still reading my suggestions are as follows:
(1) To account for the fact that both mods and the cantina tables use cantina energy, add cantina energy to the periodic energy bonuses in the activities tab. This will give players a little extra cantina energy to run missions with. You might also consider lowering the cantina energy refresh time a little bit to let people earn more throughout the day since there are now two places that require cantina coins.
(2) Increase mod sell-back prices at least 2 to 5 times the current payouts. The reality is that because mod stats are random, players are likely not getting the mods they really want on any given drop. However, I personally am not selling back any of my mods because (a) the prices are so low that I don't feel any incentive to do so, (b) I am still figuring things out and don't really know yet which mods I want and need (the stats are so confusing it is impossible to tell what some even do), and (c) I started with ALL of my characters being unmodded, so I can ultimately use every mod on someone to fill gaps. This makes the credit crunch worse, because players are not using your intended credit gain process.
(3) Consider adding mods as a rare drop from the cantina table. This would help to take away a little of the pain for those that want to use cantina energy on the cantina table.
(4) Temporarily give players an additional bonus of double the current credit awards from the mod battles and challenges. This would be just like double cantina shards and coins, but for mod credit awards. In fact, you might even consider doubling the mod drop rate so that people have more to sell back. You can roll it back in a week or two after everyone has time to adjust to the new system. This will give players a little help in getting the mods they need to balance some of the current inequities in the system.