We have talked a lot about the Baku on the this forum, but I thought it might be interesting to look at the Son'a.
These guys are not very interesting, their most heinous acts happen off screen and they seemed like a really poor follow up to the Borg.
The revelation they were really Ba'ku were not handled well (and brought up a million questions). Were the Son'a supposed to sympathetic or just evil, because you can argue the Son'a had a valid claim to the planet, but all the off screen villainy is supposed to render them unsympathetic.
It seems like they should have done something different with them: either make them more evil and give them no real connection to the Ba'ku, they are merely monstrous invaders who want to steal the secrets of eternal youth or make them more sympathetic to play up the gray nature of the moral dilemma that supposed to be at the heart of the film or get rid of them altogether and give the conflict just between the Federation and the Ba'ku.