I do agree that it is not a good investment...but it's also true that probably NO $90,000+ Model S is a "good" investment.
The price difference between the 85D and P85D is $20,000, not $30,000. With 7% tax, its about $21,400.
The speed difference is 1.3 seconds, not .75 (4.4 vs. 3.1...