I liked seeing Aldrea's opinions of Dak (and the Hork-Bajir as a whole) change as the story progressed. Originally she was only interested in Dak for his impressive (for a Hork-Bajir) intelligence, but as it goes on she starts to respect him more and treat him as an equal. I especially like the scene where she decides to go against her own people by stopping the virus.
In hindsight Seerow seems like an idiot, but hindsight makes everybody look stupid. At the time, he was simply helping a less fortunate species. That's not much different from humans looking after animals. He was a man of peace, and the Yeerks took advantage of his kind nature. I think it's a rather accurate parallel of real life, the way that nice people are often taken advantage of.