I think a model is pretty important, even cheap models set expectations of the vtuber, which they can either support or subvert through their content and how they act and behave. They also provide a visual representation for the person behind the screen and their emotions. High-quality models can catch attention when seen on corpo lineups, YouTube, Twitter, or social media and are how you are represented to other people.
Rigging's a lot less important - it's helpful if it's good but a lot of talents, even in corpos, make do with poor rigging.