Excess is relative. When you have $$billions, $150K extra to have your custom protection vehicle at the venue is no big deal. And, are they even rentable in all locales, and do you trust those suppliers?
From what I could find the 2009 Protection version (then called high security) was more around 400k-450k€. A standard model 7 runs from ~115k up to ~145k€.
Far better to take BMW's approach, upgrade the materials so that the protection is structural; each component serves both purposes.