In my experience, ECC shows benefits more often when a DIMM starts to fail, not in protecting us from cosmic rays (though I don't think I was able to make a note of the last cosmic ray that flew by me).

I've had systems limp along reliably while throwing EDAC messages every few hours. With non-ECC memory, they would have crashed and burned.

Of course, if you're seeing EDAC messages, you'd be better advised to just shut down the metal and shift your workload to a different machine until you can replace the DIMMs in question.