I am sure the offer which includes the Virgin 3 month explorer Gold is targeted to specific customers.
Nice thing is you will get 3 months taste of Gold which gives you unlimited entry to The Lounge for you and 1 guest, 2 bags free check in up to 23 kg each, priority boarding, priority upgrade , extra frequent flyer points when travelling and a few other benefits. Remember you must obtain at least 80 status credits within 3 months of being approved to keep the Gold benefits for 12 months.
A 1 way business class fare from say Sydney to Gold Coast will give you 50 - 55 status credits depending on the fare paid (about $500) , the cheapest ticket 5 and other options 10- 15. you can also earn sc's with Fly Buys 1 sc per $100 spent up to a max of 10 per month.
So, to get 12 months of Gold you will have to spend about $1000 to get 80 status credits, if you fly a bit, it is nice to have, as the lounge is great place to go to relax in and generous baggage allowances (2x free 23kg ) and even more on USA routes.
If you are already a member on Gold you will loose all of your sc's in your account to date, so if you are Gold and think you will get enough sc;s to keep Gold before your annual review date, then don't bother about this obviously.
All in all if you get approved in time for this Mastercard and get 20000 Fly Buys points as well , then it is worth it as the 20000 points value more than covers the cost of the annual fee.