I said this in another thread but here goes again.
If you get puncture and change the wheel a number of things happen (bear in mind its always pissing down with rain when you get a flat):
1, your nice sparkling unused spare wheel gets all filthy.
2, your nice expensive clothes get filthy.
3, due to 2, your seats get filthy.
4, your hands get filthy.
5, due to (4,) your steering wheel and gear knob get filthy.
6, your nice clean boot gets filthy from the wet mucky punctured wheel.
Therefore you might as well just carry a footpump, put some air in the tyre and drive to the nearest garage. Rare to get a puncture that deflates too quickly for the above solution. I never had any trouble getting to the dealers by which time it had lost about 1psi which is no trouble at all. For slightly quicker punctures you can carry some of that foam crap.
If I had a 172 I would probably pull the spare out.