Recompressing an already lossily compressed file is almost guaranteed to produce information loss, whereas storage media is getting cheaper and cheaper over time. An 18TB hard disk is now within the budget of many people, and they're likely to get cheaper still.
So if your purpose is to archive these files because they're worth keeping, buying a bigger disk may make even more sense.
So if your purpose is to archive these files because they're worth keeping, buying a bigger disk may make even more sense.