For $12k I can put up with second guessing myself for five seconds, once in a while.
Wellllll ... it's not REALLY costing $12K ... it's basically costing the interest that $12K might have earned (or might not have) less (or not) the difference between $12k and a comparable new battery.
What you're leaving out of the equation is the question of whether or not a new battery will actually be needed. Buying the replacement option locks you into the purchase of a specific battery. (Any suggestion that you may be able to exchange the option for something different is speculation.)
... But to get back to money, you still don't want to be wasteful with your original battery even if you have the replacement warranty, because the longer your original battery lasts the less you 'pay' for the replacement.
True! OTOH, some folks (me included) regard the battery as a wear item, and though I don't want to waste it, I also don't want to reduce the usefulness of it by limiting myself on what I can do with it. I would not buy any EV if I could not afford the eventual battery replacement.
P.S. I guess the one exception to the above would be those Tesla Roadster owners who have installed dedicated solar charging stations, and thus are not 'wasting' a limited resource (since a vast amount of solar energy is wasted every day when it is not collected).
Yes, but if you have a grid-tied PV system and you are feeding excess energy back to the grid, using less energy in your car means selling more to the grid and contributing (in a very small way) to the nation's energy independence.
OTOH, taking that to the extreme, you'd never drive at all. Fortunately, the Roadster (and EVs in general) uses about half as much energy per mile as a Prius.
... how many people would buy the better battery before they even need a replacement to get the improvements?
I think I would not. I bought the car because it's electric, not because it's fast, and 245 miles is double what I expect to ever need in a roadster. I have no interest in a quicker car or longer range in this kind of car. When/if my range drops below around 125 or maybe 150 miles I'll replace the battery with the same technology if it's available at a lower price than the hypothetical improved technology.
For longer trips than 200 miles, or even longer than 150 miles, I want a more comfortable car. If the Model S offered a 400-mile battery pack it would do me for my road trips for hiking in Canada and I'd trade in my Prius for it.
I'm not willing to accept the inconvenience of a 3-hour charge in the middle of a 7-hour drive (making it a 10-hour trip, which I'd have to split into two days) and where I go, fast charging is not going to be available for a very long time, so it would be more like a 6-hour charge in an RV park; again an overnight, involving leaving the car plugged in and finding a hotel away from the car. Not an acceptable compromise compared to driving the Prius.
The Roadster, exactly as it is, is the ideal daily car for me.