Secondly, almost no one who has a spare tire in their trunk keeps it inflated. That spare is useless to you unless it has 60 psi of air pressure in it. When it's low, it looks exactly the same as when it's not. When's the last time you checked yours?
Thirdly, you're better off carrying a battery jumper / air compressor "rescue pack". If for no other reason that to help someone else out. It's better than jumper cables in that you don't damage your own vehicle in the process.
1) Sorry but not so. According to research done by BMW the spare / jack / wheel bolt tool consumes slightly less than 1 litre / 100 km to carry about.
The cost saving for the car makers is also an incentive to no longer supply one and give you a 1300 number to ring (for which they will also charge you by the way) or a couple of cans of "flat fixer".
2)Why do you need the spare tyre inflated to 60 psi? I checked mine Sunday by the way.
3) An air compressor is useless if the tyre is damaged to the point it will not hold air. Personally I carry a spare and use the compressor in the garage.
I think it's dumb to exchange the spare for roadside service. There is absolutely NO way that the pennies you may save from the weight reduction will cover the tens of dollars that it costs per month to be a member of a roadside service. Secondly, if the roadside service is AAA, it's worthless anyway. When my gf's car broke down it took over 90 minutes for the tow truck guy to get there. A cop stopped after about 80 minutes and said that if he wasn't there in 10 minutes, he'd call one for us (of course he got there about 9:50 later). He also said that this length of wait time was very common for roadside service companies, and if we were ever in a busy area to just call the police because they can and will get a tow truck there within 10 minutes.
Also, I was also one of those tire guys who hated the fix-a-flat spray stuff. It made things 10 times more messy and take 10 times longer to actually find the leak and fix it because you had to wash all that crap out of the tire, then remount it to find the hole if it wasn't obvious. Then take it back off, fix it, etc....
And those run flat tires are stiff as heck and VERY hard to mount. Our technicians had to go to special training for it so that they'd know how to mount them without ruining the rims because it's very easy to scratch rims with stiff or small sidewalls.