If you think rare shouldn't equal powerful then it should at least equal unique. Plus you're likely sacrificing accessibility in order to make use of the cryosleeper.
If only they are forced spawned over 25 ly from core world which I believe it's not.
It is already a huge 10ly radius of free money planets (or rather, two), it doesn't need to be stronger.
what if also distance makes a big difference ?
planets in the same system could have population growth increase AND size limit exceeding 6 to maybe 7 or 8
and farther you're from the cryosleeper the bonuses diminishes until it only increases rate
you could even share a cryosleeper with a faction to increase diplomacy but that's probably best for nexerelin
That was the main complaint from last patch that cryosleeper only affect planets in the same system.
Now it's already overpowered but players are just going to ask for more until it become obviously OP and nerfed to ground again.
Also, you got awesome idea!
I advocate nerfing current effect to scale with distance, only full effect in the same system and -10% per ly.