There is no documented way to programmatically hide a cluster other
than by using the minimumClusterSize property.
Barry could probably get the desired effect by using
MarkerClustererPlus (an enhanced version of MarkerClusterer), however.
What you would do is hide markers that don't meet your criteria and
show those that do. For this to work, you must set the ignoreHidden
property to true when creating the marker clusterer. You must also
call the marker clusterer's repaint() method after changing the hide/
show status of any marker (or once after changing the status of all
the markers in a batch). You don't have to provide a custom calculator
because the standard calculator will include only those markers that
satisfy your criteria (i.e., the visible markers). You will never see
a cluster icon with a "0" label again.
I use this technique for my interactive real estate map and it works
great. It is one of the main reasons I created MarkerClustererPlus in
the first place.
See
http://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerclustererplus/