For small startups nothing has led me to believe that the actual taxation for a C-Corp is a major problem. But everything I've learned has suggested that being a C-Corp will definitely add significant tax expense to your life, because C-Corp taxes are complicated and LLC taxes are not.

So then the question is: of what possible benefit is a C-Corp to a small business that hasn't taken funding from an investor that requires share classes?

I'm not aware of any protection or separation that a C Corp provides that an LLC doesn't. So far as I know, the sole practical reason to incorporate a C Corp is to get share classes, which startups need pretty much solely to satisfy venture capital investors.