Mike,
Sure, most or all of these museums are non profits. But that still impedes money getting to where it needs to be. Any donation given to a museum goes to the museum - a board or a person or people that decide where to put the money. From what I've seen, that leads to neglect of some things. I know there's never enough money to go around. Museums get new things to upkeep all the time as well. There are very few places that have just a submarine as the main attraction, and even in those places there is deterioration running wild.
Volunteering these days, ugh. The world we live in of liability, insurance, craziness, makes it so difficult. Take the Drum for example. She's open to the public 364 days a year. Can't volunteer much during the day because visitors are present. Can't volunteer after hours because there are no restrooms available without leaving one of the other buildings unlocked.