@antedeluvian: I envy you all the places you've been and the things you've seen. I'm feeling a bit silly, because I've been fortunate to travel a lot myself, but in my younger years I wasn't really interested in visiting museums.
More recently, I have become interested, and I've been fortunate enough to visit a few of the places you mention, including the Smithsonian in Washington DC, the Henry Ford Museum and Greenfield Village in Dearborn Michigan, and the London Science Museum.
I haven't been to the Picasso Museum in Barcelona, but I have been to a small exhibition in Hamburg (and I quite like some of his work).
One place you mentioned that I would really like to see is the M.C. Escher Museum in The Hague -- maybe the next time I visit the Netherlands...