I use a single view for both authenticated/unauthenticated states. I have helpers for the parts of the view that are for authenticated users only.
For example: if i have a "New Contact" link that i need to render onto the view but it should only be visible to authenticated users, then i'll use my helper (something like this):
<% =Html.RenderNewLink() %>
..that helper will first check if the user IsAuthenticated
before it renders anything.
I'll have these types of helpers scattered throughout my views in the places where, for authenticated users, there would need to be more markup. And so, for the un-authenticated users, those places are blank/empty.
I hope this makes sense.. prob not the best way to explain it.