Following Andrew's reply here, I received a letter from WTP apologizing for the long time it took to process my claim, and thanking me for my feedback. Included with the letter were two checks - a full payment of my claim, and a reimbursement of my annual credit card fee.
The letter made it clear that the payments are a gesture of goodwill, and that WTP stands by its original adjudication of the claim. That is, the next time someone submits a flight delay claim where the airline states that the reason for the delay was "late inbound aircraft" (or any reason that is not mechanical, weather, or strike), it will be denied (but promptly). Since Air Canada states "late inbound aircraft" as the reason for the vast majority of their delays, this Canadian credit card is of very little value as an insurance product when flying on Canada's largest airline.
As I explained in private correspondence to Andrew, I am glad that Capital One stands behind its World Aspire product, and consider this issue resolved to my satisfaction. I might also add that, despite the rocky patches, I feel the customer service experience with Capital One ended on a high note. It speaks well of a company when screw ups are recognized and made right.
At the end of the day, however, the World Aspire Mastercard flight delay insurance coverage remains highly deficient relative to at least one main competitor. The AMEX Gold Rewards Card, for the same annual fee and with otherwise very similar benefits, covers *any* delay regardless of what the airline states as the reason (with the usual exclusions of terrorism, war, and nuclear reaction). Because of this, I cannot rely on the World Aspire Mastercard as an insurance tool for my considerable travel spend, and cannot recommend it to anyone in search for a card with travel insurance benefits. I will continue to use this card and its excellent rewards program for all my non-travel spend; I hope the folks at Capital One review and update their insurance coverages so as to make their product competitive on that front again.