Michael Dorn just walked on set.This film offers no explanation for why Worf is in it. He literally just shows up and they go with it. My guess: Michael Dorn initially refused to do the film, but got lost on his way to the set of DS9 and happened to walk into Patrick Stewart while filming that corridor scene in the opening. Why waste such a good take when you can just throw him in.
There was supposed to be a Goose That Laid The Golden Egg metaphor that got lost somewhere in the movieDestroying the planet would likely have killed whatever it was that made it so rejuvenating (or reduced it to a comparative short term effect).
There is another way to harness the radiation without destroying the Ba'ku homeworldThe Enterprise crew starts to feel the effects of the radiation the MINUTE they enter the Briar Patch, and Picard even says that it's all over the region. Dougherty just didn't want to wait to find it.
The Baku will be able to save the Son'a.The Baku have lived on the planet for three hundred years and probably built up a ton of that metaphysical particles in their bodies. The Son'a are the same as the Baku only really sick. Dr. Crusher could probably have the Baku donate blood or bone marrow (with their permission) and transplant it to the Son'a. It could speed up the healing process and help save their species.
The Baku and the Son'a are humans.If nothing else, it would explain why the Baku are identical to humans - that they were human colonists themselves. Similarly, the Son'a's appearance isn't a greatly exaggerated pastiche of plastic surgery and other methods used to preserve a youthful appearance, and their delayed reaction to the planet's atmosphere would simply be because of their advanced age.