A good question.
A local answer.

Check whether any airport-specific ticket offer applies to a city trip before paying for the wrong product.

Check the arrival time against current service hours and allow for immigration before choosing a fixed departure.

Compare the total cost and time to the exact cruise terminal, not only the flight. The final terminal transfer may need a taxi or booked car after public transport.

Check weekday traffic and any current M1 works for your travel date. An early departure gives more margin than aiming to reach the airport exactly when bag drop opens.

Use Translink and Airtrain's current planners for your exact date and time. Rail works or replacement buses can change the route, so do not rely on an old forum fare or timetable.

Use Translink’s journey planner for your actual Brisbane starting point and Gold Coast address. Trains reach Gold Coast rail stations, and the G:link tram connects at Helensvale for many coastal destinations. If you are starting at Brisbane Airport, check Airtrain’s separate…

If most days are around the coastal tram corridor, choose accommodation near a current G:link stop and use Translink's journey planner for the rest. Check the exact beach or restaurant address: the coast stretches well beyond a single tram ride.