MY Performance gets faster acceleration, higher top speed, 21" wheels, performance brake, and a spoiler. Would anyone pay $10k for that? Compare this upgrade to any traditional day manufacturer, it's a bargain (just check out Porsche 911 vs 911S vs 9114S...etc). But is it necessary, that's for the individual to decide.
I believe your argument is that software upgrade doesn't hold a value or worth as much as a hardware value. I think that's a highly debatable topic. As for FSD, I can see your point (and agree) that you own the software and you should have power to take it with you to the next car.