Rather than just deleting accounts that go over the maximum inactivity limit, why not make their planets become NPC planets that slowly degrade and automatically get deleted after a certain amount of time.

This would also increase the availability of raiding targets.

Of course, the NPC account would have techs that are higher than most players and spawn new fleet every so often, to keep it from being too easy.

This would be quite hard to implepent, but i like the thought of it. I believe i suggested something similar a while back

Adding comp players hmmm...could work as long as they don't become too challenging.This is a MULTIplayer mmo after all.