I was told by someone today that he received 5 SP when he signed up and that it was also suppose to be worth $10. So they did adjust the promotion reward for signing from 5 SP down to 3 SP after the price went up, and just forgot to adjust it again after the price went back down.

Of course would it feel right, because it would have the same value! $10 are $10. We still live in a fiat world, so the only thing that matters is a fiat value. If everyone who signs up gets something with a $10 value it is as fair as something can be.