I've cooked on my oldest/rarest (solid triangle) only once. I haven't cooked on a NIB Copper I bought last year, but only because I haven't even gotten it out of the house yet.
Maybe I'll break it in today w/ a cod cook. It will be it's first cook and my first cod. Might get interesting.
I have a '98 Blue MT set up for rotis. that is used relatively often.
My attitude is I will cook, albeit rarely, on a rare kettle. That's what they're there for.