You should be able to revert to points if you select the current value
and then type in a value in points.
FWIW, what you are seeing is specific for the "line" unit. Typing
anything else in the boxes, such as "li" (for lines) or "cm" (for
centimeters) would cause Word to convert to the corresponding value in
points, the next time you visit the dialog.
Hmm... I just did some testing with the macro editor specifying "line"
units for Spacing Before and Spacing After. It seems as if this has
something to do with Asian language support (there are LineUnitBefore
and LineUnitAfter properties in VBA which are referred to by VBA Help as
specific for Asian languages). If you cannot make the units change to
the default by simply typing in different values, you probably have to
take a look at the language settings for Office. For instructions, see http://homepage.swissonline.ch/cindymeister/LangFmt.htm -- se especially
the section titled "Enable only the languages you want to use".