Instead of adding co-hosts, why not just have the guest judges in on the coaching sessions? The shows would get a better idea of what the judges will be looking for and the judges might have chance to actually know what they are about beforehand. Sometimes I think the shows get judged unfairly, due to the guest judges being completely unaware of what they are about to listen to.
Also, I think the guest judges should be more related to the challenge of the week. I mean, I love Tig Notaro, but why is she there during the sketch week? Similarly, Matt Gourley was there during the recurring segments week, and he does a sketch podcast.