GG
You are correct in that the wings break at the aileron inboard end in the downward mode. It occurs beyond vne due to the large washout inC210 wings. I've never heard of one breaking up where there wasn't some sort of control loss leading to an excursion outside the envelope.
A C210 spar is just as strong as any other type in it's class and is actually stronger than the early strutted models. The low Va is a sensible precaution to give a large margin before vne in rough conditions.