One list or two for members and non-members?

I'm trying to understand the best way to manage lists for a website with paid membership.

If there is a broad list that anonymous users can sign up for and a separate list synchronized to authenticated members, doesn't one have to remove members from the broader list to avoid sending duplicate emails to members and everyone else?

On the other hand, is there a way to manage one list and target just authenticated members (or members with specific roles) for certain emails? Could one use segmentation and a field that indicates paid members in some way? Is that possible now or is that a feature request?

It seems cleaner (and potentially more cost effective) to me to have one list rather than two, but is there a reason to prefer a two list solution?

Finally, does the preferred solution change if there are special interest groups that both members and non-members can be part of?

Thanks.