The title Animal Dreams is a reference to a specific conversation about the dreams Jack the dog is having as Codi and Loyd lie around having some post-sex snuggles in the middle of an archeological site. Let's give it a gander.
Loyd asked, "What do you think animals dream about?"
"I don't know. Animal heaven." I laughed.
"I think they dream about whatever they do when they're awake. Jack chases rabbits, and city dogs chase, I don't know what. Meter readers."
"But that's kind of sad. Couldn't a dog have an imagination, like a person?"
"It's the same with people. There's nothing sad about it. People dream about what they do when they're awake."
[...]
I studied his face. "Didn't you ever dream you could fly?"
"Not when I was sorting pecans all day."
"Really, though. Didn't you ever fly in your dreams?" Even I had done that, though not often.
"Only when I was real close to flying in real life," he said. "Your dreams, what you hope for and all that, it's not separate from your life. It grows right up out of it." (12.151-160)
Animals dream about what they do all day. In the beginning of the novel, Codi finds that a little sad—she wants to use her imagination; she wants to fly; she wants to escape. Big surprise, Codi.
So what does chasing rabbits have to do with saving small desert towns from environmental disaster? Consider this statement from the novel: "[T]he very least you can do in your life is figure out what you hope for. And the most you can do is live inside that hope" (23.178). This novel is anti-heroism—by which mean not that it hates heroes, but that it thinks real heroism is in the small details of day-to-day life.
Just as Jack the dog dreams about what he does all day, figuring out what your dreams are and just going after them every day of your life is the best possible outcome for characters in Animal Dreams. It's not that Kingsolver is against imagination; it's just that imagination in this novel is grounded in what we do in life.
What that means is that Codi and her friends and family save their town not by heroic, crazy acts of sabotage but just by writing letters, making piñatas, and ultimately getting Grace on the historical registry.
On the flipside, Hallie dies at the hands of the contras not because she meant to go be a martyr in Nicaragua but because she couldn't do anything other than use her skills to try and help people—that's just who she was. As Codi puts it, quoting both Hallie and Loyd, at the end of the book, "It's what you do that makes your soul, not the other way around" (27.46).
Way to sum up the themes of the novel, Codi. That's deep.