Just because you say the debate should be ended doesn't mean it's true, or that you are even correct.
To end the debate, my staff master electrician says just replace the breaker.
Your staff electrician missed half the answer, which would be to replace the breaker AND the receptacle. But you make sound as if the OP has that option readily available to him, and it's doesn't answer is original question.
You can leave the outlet if you want or replace it too.
Really, a mismatched outlet on a breaker size not intended for it? That seems like a good idea.
Doesn't matter. The 30A circuit should be 10 gauge which is fine for 20amp.
That part is correct.
And to Jay: Network cables most certainly do carry power.
No, they carry signal, which is considerably different - unless of course it is 802.1af.