Though we are a natural history museum, we sometimes have related art exhibits
and have loads-o-experience with exhibit openings.  The informal report is:

We change temporary exhibits approx. every 4 mos. though some are here for
2 mos. and others for 6 mos.

We have opening receptions for most except maybe the very smallest, low-budget
ones.

Typical attendance is 200.  This is about average and satisfactory.  Weather
is the biggest impact--if it is bad we have lots of no-shows, because they
have not paid to come.  The more exciting the exhibit or "communal" the topic
the more attendees we have (i.e. a Star Trek exhibit we had had hundreds of
Trekkies who do not normally come to our events, same with a Chinese and an
Hawaiian exhibit--those communities came out to support their members).
Has not made a big difference where the exhibit or "artist" originated from,
but more subject that influenced attendance.

To increase attendance, we invite the "community" the exhibit would interest
as well as our usual roster of donors, etc.  We are not necessarily interested
in huge numbers at our openings as we are paying the expenses, but like a
good crowd for energy.

Most openings are Tuesday or Thursday at 5:30 or 6:00 pm; press openings are
always a weekday (not Friday or Monday) in the morning as most press do not
work evenings.  Public openings are always on a Saturday.

We consult the social calendar to make sure we do not have openings on same day
as another organization's fundraiser or big event.  Is good idea not to compete
unless you think the two audiences are mutually exclusive.

Our openings are primarily to thank sponsors and donors to the exhibit,
cultivate potential donors, promote the exhibit, give recognition to staff
who worked on the exhibit and artists etc.

"Ideal" way of conceptualizing openings is deciding what the purpose of the
opening is (ie to cultivate donors, thank donors, promote artists etc) and then
plan the opening around achieving that purpose.  If you want to cultivate donors
you need alot of staff and/or docents to give them individual attention and have
good follow-up.  The way you serve the food will allow for conversation and not
separate you from them.  Being thematic and having entertainment to go with
the exhibit enhances the experience and makes it more memorable and individual.
We try to make it an Event! not just an opening.