Perhaps the insurance company was able to get the used Porsche at wholesale prices, thus saving themselves a bit of money. From their point of view, it's almost all basically the same as cash equivalent, so I don't see why they'd bother with something other than cash unless they want to keep the customer happy or can actually come away spending less.
Correct...an insurance company can elect (if you are in agreement) to replace your car with one of like kind & quality, but would only do so if an acceptable vehicle was available and the cost of acquiring this vehicle did not exceed the cash settlement offer.
The key is that most comprehensive insurance covers the blue book value of your car during the period of coverage. Each year, or period, your premium goes down because the maximum amount they're going to pay out drops as the value of the car drops. If you have a very old car, say, twenty years old, then the blue book value is going to be very small compared to the cost of replacing the car, assuming that it is rare and unique. If you maintain comprehensive on a very old car, and it gets stolen or totaled, then you're going to be in for a huge shock when you look at how little you get. On the other hand, if you have a brand new car, the coverage will probably be almost enough to buy a new car. There are various clauses for replacement cost insurance, but I don't know whether they cover exotic cars - certainly not by default.
In Ontario, we have no true "replacement cost" option for auto insurance. Most companies will sell or include the #43 endorsement (limited waiver of depreciation) which guarantees that your settlement amount will not depreciate from the sale price of the car. It is important to note that the #43 endorsement ONLY applies when you are the first time buyer of the vehicle (a new...not used or a demo) and ONLY if the loss occurs within 30 months of you purchasing the vehicle.
I do wonder if you can specifically ask for more coverage than the default. At the very least, you can talk to your insurance adjuster about these various "what if" questions to see. Since each policy and company differ, it's hard to say exactly what would happen in any particular case.
These specialty endorsements that deviate from ACV indemnity are not rocket science...I'd be shocked if most companies did not offer them...the key is asking your questions of your insurance provider now( not later, after a loss occurs.)
One thing to look out for (in my opinion) is that your VIN records will show that your car was totaled, even if there was no wreck or other structural damage. If enough parts are unscrewed from an old vehicle - enough to match the blue book value of the car - then the insurance company will total that car even if it's perfectly drivable (albeit missing several parts). Sometimes it's better to just talk to your insurance adjuster and accept a smaller check from them just to avoid having your VIN marked as being totaled. That can certainly harm the resale value unless you find a trusting buyer who'll believe that 'totaled' is not the same as "severely damaged."
P.S. If the Tesla Roadster does actually increase in value in the coming years (somewhat doubtful), and particularly if the blue book values honestly reflect this increase in value, I wonder whether that means our premiums will go up to cover the insurance companies having to protect themselves against paying out more each year. At the very least I'd assume that if your premiums are dropping then your coverage is dropping at the same pace, and thus you'll be in a bind if you have to replace. I suppose one part of the answer is to look at the Kelley Blue Book history and see whether any cars actually appreciated in value above their original, new purchase price. If so, what have insurance companies been doing about these kinds of very special cars?