The larger address space is only an advantage if we don't need a v4 address. The situation "I need a v4 address" is not worse than the situation "I need a v4 address and a v6 address".
Not exactly. There's some pretty snazzy interoperability tech out their. (I.e. 4-6-4 XLAT) that let's clients get v4 addresses when they need them, which means if there's a big chuck on devices on both ends that support v6 you don't need as many v4 address.
This kinda a problem for motivating people to move to v6 because as implementations of v6 grow there's going to be less and less pressure on the v4 address space.
