Another tip is to try to limit your expansion while going after the shards: Each shard appears several planets deep in AI territory. If you take the intervening planets, the next shard will lilkely appear even further away, and the slow return trip gets longer and longer, with more and more territory for you to defend.
Instead of that, don't persue the shards past the colony ship mission or so, until you've taken a good hunk of territory and set up some solid defenses, maybe a chokepoint or two.
Then, send out your fleet and neuter all the planets on the way to the next shard location, but don't take out the command centers. This makes the trip home easier and gives the possibility the next shard will be found along the same path of already-neutered planets. Or at the very least, you won't have to clear out another 4 planets in this same direction.