I don't see why any WHM would want this piece ><.... it's only real good feature is... 5hMP, same hMP you get from Errants. This piece has no natural refresh yet costs alot more then pieces that do have a natural refresh...
Well, one reason would be the higher +enfeebling magic skill, granted it's only 2 more than regular AF body, but it's the most WHM can get from that slot. Not a huge deal for HNMs or exp, but it might help out in certain missions or other situations where there's nobody better to throw out Slow/Para/Silence/what have you.
That being said, I think you'd be much better off upgrading other AF pieces first (Hands for Hexa Strike seem to be the most popular, followed by Head for +MND Cure V boosting).
Limbus drops the coins and items for the AF1+1 upgrades. In order to obtain the new AF2+1 you need to obtain both the AF2 and the AF2-1 from one of the new dynamis areas and pay a fee in dynamis currency
It's all Limbus related, if i'm thinking correctly. I've never done Limbus, so I have no further info on exacly how, but i'm 99% sure Limbus is where all the AF+1 sets stem from. Hope I helped a trifle. =)