This is confusing.
So, let's get this straight. If the So'na were to harvest the power of the planet, they would be able to rejuvenate themselves and live forever? If this is true, doesn't that mean the Baku could also use the power properties and continue to be immortal long after leaving their planet? If that's true, then what did the Baku have to complain about? The only thing they would be missing out on is their village, but they would still be immortal. For that matter, everyone in the Federation would be immortal. So why did the Baku insist on not leaving?
Please correct me if I've gotten something wrong (which, more than likely, I have)
You've got it wrong. Using the particles will double someones lifespan with the S'ona method.