No experience on baggage side of things...
But I have flown QFi Au - NZ after 2012, and have earnt both my own and my other "friend's" QFF points and QF SC.
The latest was about 2015 I think if I remember correctly.
If they changed the rules after that, then my idea would be out of date, but...
Just on the space factor, and if you can afford it, even if no extra QFF points or QF SC earnt, I would get the comfort seat booking in place.
Being able to lift up the handrest without having a behemoth next to me was a great thing.
Some people on a flight will spread their legs out wide into your space, and hog the arm rest, and then take over your space as well.
Granted that sometimes the comfort seat booking might not work, you get onto the plane and find your request, even if you had bought that empty seat next to you, to find someone in it.