When using a view in "Unformatted list" format with inline fields, how can I most cleanly add a break between the fields?
I would say CSS is the better route because it separates your content from your layout just as CSS does with respect to HTML.  Also, if you decide to change your layout later on, CSS will most probably be easier (and more obvious) to change than some fake data in a view forcing that is forcing/hardcoding your layout.