One of the things they want is for identities to cost some nontrivial amount of money, about $10 or so. This mostly solves the spam problem because it's unlikely that spamming will get you $10 worth of value before you're blacklisted by your parent star and it refuses to route your packets.
Can you think of an identity count that would preserve moderate scarcity like this? Or would you have the address space be indefinitely mineable, kind of like bitcoin?