In regards to your question of museums' goals.  Although I am taking a risk and sounding wishy-washy, it is a question each individual museum must answer for themselves.  The goal, or focus, of a museum is as unique as the museum itself. Yes, we must stay in business as once traditional funding is becoming harder to secure.  And a museum should always strive to maintain an open lines of communication with its constituency.  Which leads us back to the museum's focus.

I am a director of a new industrial technology/history museum.  The museum was created because industrial heritage of the county and continued reliance on manufacturing.  As we are new, and still developing our collection, education is our focus.  We cater not only to the schools and technical college but to our general public by demonstrating about past and current industrial processes and local companies.  Down the street is the National Heisey Glass museum.  Formed and partially funded by the Heisey Collectors of America, this museum's focus in on its unique collection.  Both museums have a niche, local and national, which is derived from their focus or goal. Maintaining this focus will determine the financial support by that museum's consitutency, whether it is through  membership, corporate sponsorship, foundation grants, or admittance fees.

Basically every museum should always preserve its collection, educate, and create accurate and eye-pleasing exhibits.  However, the primary focus should be well thought out and be determined by the museum's nature and need within the community, local or national.  It is what ensures an importance within that community and the resulting financial support.

Of course, that is just my opinion

-Brian