Hello, John!  We are dealing with the same challenge with our new
facility (opens fall, '99).  A variety of solutions have been suggested,
including:

1.  Reserve the two classrooms during the lunch period for groups that
need them (no programs at that period, say 12 -1 pm).

2.  Encourage groups to eat outside on the grounds, which will have
facilities such as an outdoor amphitheatre designed for this & additional
purposes

3.  Encourage groups to eat at nearby parks & restaurants

4.  We have made vending available for groups but will not encourage them
to use our cafe (much like yours, I think)

I am sure that we will make adjustments and we have a bunch of factors to
consider.  For example, we realize that if we schedule a lunch period in
the classrooms, we will lose a program period a loss of opportunity, and
loss of income (a harsh but realistic concern).  After we see how it
goes, we may encourage certain groups to use the cafe (e.g., smaller
groups that come for an all-day, in-depth program).  Another factor:
community restaurants would like to have us send the group their way.
Our community did put up $5 million towards our new facility, so we are
mindful of helping them out.

I'd be please to discuss this with you or anyone else who is interested.
Our two museums share similarities of size and focus