Are your exhibit guides just standing there waiting for questions?  You
might try having them do exhibit-related demonstrations periodically, as a
way to get them interacting with the public.  Many people feel very
uncomfortable approaching a visitor to ask if they have any questions.  If
you can give them some sort of ice breaker, you will probably get much
better results.  The demos don't have to be complex.  In fact, simple is
better.  For example, if you have the classic "Hand Battery" exhibit, give
the guide a cart with some dissected batteries, to show how they compare
with what is happening in the exhibit.  The same technique can apply to
history and art as well as science.  If you want to "bat some ideas
around," let me know.

Robert Krampf
Science Education Company
http://members.aol.com/krampf/home.html