What's the main goal of a museum?

This seems like a simple enough question, but it has hidden layers.  For some museums (Banana Club Museum, I'm lookin' at you...) the aim is simple: collect items around a central theme and display them.  They are not on the cutting edge of banana research, they are not preserving important banana artifacts that would otherwise be destroyed, they're not making the public aware of the long cultural traditions of the banana.  They're just collecting banana stuff, putting it on display, and inviting people to come take a look.  It's not a bad thing by any stretch--those little museums can be a lot of fun.  But it allows them to skirt some of the deeper, more existential issues other museums can get caught up in.

For example: is a museum's primary purpose to preserve artifacts, or to educate the public?  Should they focus on conservation, or exhibitions?  Is it better to teach the visitors something new, or to make sure that they enjoy the time they spend at the museum?  Should new research take priority over increased publicity and marketing?

It's a chicken-or-egg conundrum that goes back to some of my earlier questions.  You can't maintain collections without a source of revenue, and you can't bring in enough revenue without appealing to paying visitors (or getting substantial private or government funding).  So how should a museum prioritize all of those important facets?

Personally, I'm torn.  As I mentioned last week, I owe my career and love of museums to a program that many institutions might see as superfluous.  I'm sure if you asked the curator in charge of the hall where I fell asleep in my green sleeping bag after a night of exploration, he would rather have more money for the preservation of the artifacts I was entranced by rather than education programs that allow 6-year-olds to scare themselves silly in mock Egyptian tombs.  But coming (as I do) from a retail and visitor-oriented background, I can't help but seeing the interaction the public has with a museum's collection as equally vital to an institution.  ...Well, maybe not equally vital.  If I was told that an artifact would deteriorate beyond repair if it was put on display, but could be used for research and study if kept in storage, I could accept that.  What I think I couldn't accept would be not making an effort to serve both purposes.

What do you think, small, but apparently loyal readership?  What facets of a museum are the most important?  When tough times hit, what gets cut and what gets saved?  It's only a partially rhetorical question--many institutions face this exact choice right now.