Is there a valid reason to carry the extra weight of spare tire? Will roadside assistance show up with tire mounted to wheel and then change it? There is no way I could change it myself.
At the very least, carrying an unmounted tire will keep you from being at the mercy of the guy that KNOWS he has the only tire of the correct size in the county, knows you're stuck, and is ready and willing to ream you for it.
Personally, I carry a mounted spare (11R22.5) and the tools to change it.