Hello Qantarse, welcome to the forums,
Need a lot more information to be reasonably precise, but I'll make assumptions to kick things off.
I can't find a QF flight MEL-BKK, looks like its Jetstar only. I'll assume your trip is discount economy so no points to be gained there.
BKK-LON return = 11,800 FF points, 80SC, again, assuming discount Y and no FF status. I value my QFF points at 3c each, so, to me, those FF points would be worth AU$354.00. Status credits have value too, for those interested in status, I value mine at about AU$1.00 each, though I know others who value them a lot more highly, even 5-6-7-8$ each. For me, I'd add $80.
All up then, points value for me would be= $354 + 80 = $434.00
You'd have to make your own decision on whether its 'worth it' depending on your overall travelling strategy. I wouldn't fly JQ so the point is moot to me.
[edit: Again, depending on your strategy, MEL-SYD-BKK-LON return might suit you. Gets you off JQ and makes the trip 22,000 FF points + about 160 SC. QF + BA Codeshare + BA all the way and tickets available mid Sept. at under $2200. FF points + SC in my calcs = $660+$160=$820 of value and the ticket face value is the same as TG]