Note spacing changes that don't register

[Mus Felix]

I have a long passage of music made from many different sections, some with
very short notes and others with long notes.  To overcome the spacing
oddities that naturally result I have tried manually setting the spacing for
each section.  However it seems that this setting gets applied only once for
the whole score and all other calls are void.
See the following example (there is a different spacing setting every 16
bars, but it all comes out the same):

\version "2.13.51"
\include "english.ly"
\relative c'
{
   \override Score.SpacingSpanner #'spacing-increment = #'1.2
   \override Score.SpacingSpanner #'common-shortest-duration =
#(ly:make-moment 1 2)
   \clef bass
   \repeat unfold 16 { c2 c4 c8 c16 c } \break

   \override  Score.SpacingSpanner #'spacing-increment = #'1.1
   \override  Score.SpacingSpanner #'common-shortest-duration =
#(ly:make-moment 1 8)
   \repeat unfold 16 { c2 c4 c8 c16 c } \break

   \override  Score.SpacingSpanner #'spacing-increment = #'1
   \override  Score.SpacingSpanner #'common-shortest-duration =
#(ly:make-moment 1 32)
   \repeat unfold 16 { c2 c4 c8 c16 c } \break
}