Credit card insurance is a minefield. Always read the ‘eligibility and activation’ clause before assuming any cover. Most cards I have encountered require you pay either the full return fares or a high portion thereof.
Some eg. Amex allow you to use their points…an extract from there T & Cs
‘Cover is effective when You pay the full fare for a return Trip on the
American Express Explorer™ Credit Card or with American Express
Membership Rewards® points or with Travel Credit.
The Trip must commence and end in Australia. Cover is not
activated until a return ticket has been purchased (i.e. if You only
hold a one-way ticket, You are not covered under these benefits).’
Some don’t eg. ANZ credit… an extract
‘Interstate Flight Inconvenience Insurance
Interstate Flight Inconvenience Insurance is available to
participating cardholders whilst they are on an interstate
Australian holiday of up to 14 days provided the participating
cardholder charges the entire cost of their return interstate
flight fare (but not necessarily the associated taxes, airport or
travel agent’s charges) to the participating cardholder’s
participating credit card account.’
and NAB credit extract…
‘You (or the accompanying NAB Cardholder) had purchased on a NAB Card 100%* of your return interstate airfares prior to the commencement of the trip.’
Your solution by purchasing a ticket then upgrading using points is worthy but needs to be compared to simply taking out a travel insurance policy for that travel. If you are in good health it can be a cheaper option.
I personally have never been in a position to rely on credit card cover for travel insurance and have paid for private cover. My advice is to look closely at the cover you require then check to see if your cards are appropriate.