.45 +P brass does indeed have a stronger construction than regular .45 brass according to Starline. Interestingly, this not the case with .38 Special +P and 9mm +P--for these the regular cases have the exact same strength and construction as the +P cases. Starline also indicates that .45 +P cases have 2 grains less internal capacity than the regular .45 cases. In my experience, .45 ACP cases can be used nigh on forever -- they just never seem to split.
If you want extra-strength brass for your regular .45 loads, you might as well buy .45 Super brass. Although as I said, I think you'll find regular .45 ACP brass never really wears out.
Regarding safety -- if a load's not safe in regular .45 brass, I wouldn't count on .45 +P or .45 Super brass to save your bacon.