For me it's a no brainer, I'd go ahead with the status run if you can. Think of it this way, how much are those 120,000 points worth to you? For me that's a business class flight between Sydney and the US west coast, certainly worth more than a the marginal benefits of Platinum status. And as you rightly pointed it, the extension will do nothing to get you closer to lifetime Gold status which arguably is the holy grail we should all be striving for.
The other thing to consider is of course how close you are to loyalty bonus this year, where you can select 50 bonus status credits after every 500 status credits earned through Qantas flights (excluding the bonus status credits from a double status credit promotion). What's interesting here is if you earn that loyalty bonus towards the end of your program year as you can apply the bonus status credits to the following year. For instance, if your year ends in April, and you earn the loyalty bonus this month, then you would have until the end of June to select your bonus status credits. Depending on whether you have green tier status, it may be possible to even start the year with as much as 150 status credits (50 status credits from loyalty bonus this year applied to next year, 50 status credits from green tier earned this year but applied next year and 50 status credits earned from green tier next year applied in that year).
-RooFlyer88