Hi all, OP here...
Back home now... I agree with many that, although sharing the middle seats with a stranger can be anywhere from a lot of fun to slightly awkward, it is still much better than a WT+ seat on a 13 hour overnight flight...
I boarded and got settled in my E seat, and immediately pulled out the (very small) divider. Soon after, it turned out that the F and G seats belonged to a Singaporean couple, around 40 years old. Apparently the F seat was officially the lady's seat. They started talking (quietly) to an FA, but I could easily understand that they were asking the FA to ask me to switch seats with G. I said yes before she even repeated the question to me. They then started talking quietly amongst themselves again, apparently after having another look at the situation. They then said they didn't want to swap anymore, because she preferred to be in an aisle seat. The gentleman then got settled in F. I wondered for a moment whether it was appropriate to change into my F "sleepsuit" (which I usually do on long flights in CW, since I feel much more comfortable that way and sleep much better), but I did and slept rather well. Much, much better than I would have slept in WT+, that's for sure! And probably better than in an aisle seat.
As for the lounge situation: as others have mentioned the Qantas lounge is much, much better than the BA lounge. Huge size, many different places to sit, good food (both buffet and freshly prepared), nice enough Australian wines, cocktails. Wonderfully friendly staff. No real champagne though, which is probably the only plus for the BA lounge. BA lounge was completely full with a 777 and a full A380 leaving within 30 minutes of each other, while Qantas lounge was nowhere close to capacity. I wonder how many of the BA passengers actually knew they could also use the Qantas lounge...