One of my favorite things about dogs is all of the different noises that they make. Sure, there are standard barks, but there are also howls, whimpers, and what I swear is laughter. They can be so expressive while not using any English words. They are masters of clownery, in the classic French sense of the term.
But if dogs could talk, I think it would only increase their lovability. After all, one of our favorite genres as a culture is the talking animal movie. We can't get enough of them. But if all dogs could magically talk, I think there might be some hurt feelings. Maybe we'd find out that they're actually talking smack about us behind our backs. Maybe we would find out which friends of ours they approve of and which ones they don't. It might start a revolution that we wouldn't be able to undo. I'd still risk it, just to hear what kind of voices they'd have. It'd be worth it.