My pets express themselves pretty clearly, despite having much more limited ability to communicate across species lines.

They express wants and needs, not emotions. Assuming that they have emotions that are the same as human emotions is anthropomorphization. They might have some analogous emotions, and boredom in a mammal might seem similar to human boredom, but where do you draw the line? Can a dog experience ennui? Can a cat experience a lack of fulfillment? Can a snake experience depression?

I feel reasonably confident in stating that I believe animals are conscious, just to varying depths.

I don't disagree, but you can't say that animals that evolved consciousness in completely different environments and with different senses and neurology would experience emotion in the same way as humans. Apes, sure, they are really close and probably the easiest argument for human emotions in non-human species, but other mammals get farther and farther from human experience and emotion, and it's presumptuous of humans to assume that they experience emotions the same way. Read "What Is It Like to Be a Bat" for some of the philosophical and scientific issues with assigning human emotions to other mammals.

And other intelligent animals that are further removed from humanity on the evolutionary chain would have even more alien emotions. Humans can feel empathy for an octopus or African Greys, but can either of those animals feel empathy for humans? What about curiosity? They seem curious, but how can we know if they experience curiosity that is anything like human curiosity?