This. $500 deductible and $2500 max unless I can prove I had no knowledge of the leak, then $25k max. Not sure how I could have known or, if I did know, why I'd let it deteriorate to the point of rot, but, I'm guessing it's a safe bet they can find reason enough to deny. Plus, like you said, not worth the claim baggage when there's no way there's more than $3k worth of damage.
It just sucks.
Your electrical box is no different than an old roof. Just because it is old and a higher hazard doesn't mean the insurance provider should replace it to avoid future further loss.