QF1 in a couple of weeks. (27/06)
SYD-LHR, SYD-SIN, or SIN-LHR?
Your cash bid will almost certainly be unsuccessful as all classic upgrades are processed first, like you've mentioned. On top of that European summer is one least likely times to get an upgrade on QF1/2, although your Platinum status is going to help a lot if you can find enough points to submit a classic upgrade request.
If you are prepared to fork out $1600, you might consider calling a
Qantas Wine advisor and negotiating a deal for 2 or 3 cases of
Cape Barren Shiraz for $1200/1800. You should be able to get 10-20k extra points* for a first order of this size with Qantas Wine, in addition to the 60k/90k bonus points. The points arrive in 2-3 days of ordering.
You then have 20k (existing) + 60/90k (public bonus) + 10-20k (first order bonus) = somewhere between 90k and 130k points. Classic upgrade rates are below, you may even have enough to apply for a J upgrade.
SYD-SIN: 34,100 (W), 54,500 (J)
SIN-LHR: 47,600 (W), 76,300 (J)
SYD-LHR: 81,700 (W), 130,800 (J)
Worst case scenario your upgrade is unsuccessful, you have plenty of wine to help forget the horrors of long-haul economy, and a decent stash of points for your next trip.
Another option is to ask family members if they can lend you points? If your upgrade is successful then buy the wine to repay the points, if unsuccessful just transfer back to the family member.
*Just ask if there are any promotions available for new customers and/or large orders. In May they were running the following promo
spend $2,000 or more on wine in one transaction at Qantas Wine via the Wine Advisor service, and receive a bonus of 30,000 Qantas Points, on top of the standard points per dollar and any bonus points earned. Plus for every additional $1,000 spent in the same transaction you will earn another 15,000 Qantas Points (up to a maximum of 90,000 points)^.