web 2.o. Should I Use A Unique Article For Each Web 2.o Or Just Spin?

Let's say I hire out a link pyramid to someone. What kinds of questions should I ask them or things should I check to make sure the spinning is done correctly?

Why are people saying 70% is a good # to have unique?

If google is so good at determining spins, why does it matter what % it is at?

Why does the content need to be readable? Why doesn't unreadable content 99% spun work? Google has an algo. that checks for grammar I'm assuming?

Unique is always better but having just unique articles can be expensive. But if the articles are spun really well, it also works as well.