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.
The Ba'ku are lying about not using technology.Come on! Even the Organians from the TOS episode "Errand of Mercy" put on a more convincing facade of a pre-industrial, agrarian society! The Ba'ku village is so perfect, so immaculately clean and white, that it looks like some sort of New Age vacation resort! The Ba'ku go about their labors with a casual ease that suggests that it takes very little effort to complete all the tasks required to maintain the village, grow food, make clothes and other goods. They come across as hobbyist "farmers" with a weekend home in the country! There's also the standing question of how they kicked the Son'a off-planet and keep them from simply coming back. Granted, the Son'a show a lack of will to kill their kin, but it's a planet. Pick a scenic spot a thousand miles away and build a settlement of their own! The Ba'ku know that they can score more sympathy for their "plight" if they pretend to be non-technological. So they conceal their technology to give the impression that they are a simple, rural people who should be protected by the Prime Directive.