My comments on this.
I tend to agree Cubes. Every car manual (as in the one with the car) I have read have said 'use moderate acceleration, for best fuel economy' Not light not heavy.
Being smooth also helps. Try and get good control. Being in cars with other people they are constantly on off on off, it adds load, uses more petrol. It also is really annoying.
I also (up to a point) drive by my boost gauge. Feel the car, you can feel when its straining, feel when its not doing anything and its time to change gears.
I feel I can say this as Im getting 550-600kms out of my RB20DET cefiro (so heavier than most of you skyline boys) Say 300kms of that is highway to be honest, but its still not bad.
In regards to the lounge room stuff... Personally I know 40* ambient (hotter inside of the car) in QLD summer is NOT safe. When you get that and rain, windows down dont work, you get wet. A/C is a MUST for Qld. You cant think straight otherwise, make mistakes, and crash. Ditto with stackers. The idea is so you dont need to change CDs while driving, being safer again. I do a lot of driving, and listen to music the whole time, so I can justify the extra weight and use of engery for that. As I say tho, thats just me...