Based on statistics that Shog9 kindly provided we get only a few answers from unregistered users and most of them are bad*:
the past 60 days worth of Mathematica answers produces:
Registered Unregistered Registered Badness Unreg Badness PctRegBad PctUnregBad ---------- ------------ ------------------ ------------- --------- ----------- 1659 17 128 13 7.72 76.47
In light of this and given that we have no backlog of review items I propose adding answers from unregistered users to the Low Quality Posts review queue.
* Shog9: "I'm gonna define a 'bad' post as one that has been closed, deleted (by someone other than the author), or down-voted below zero."