Hi Steve - you can use the ShrinkTrimmedSrf command to remove excess control points from the outside area of an underlying surface that has been trimmed:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#shrinktrimmedsrf

But there isn't any easy method for reducing control points from interior areas of a surface, I think that there are some options for controlling the density of the generated surface when you construct it from ZSurf though.

- Michael