Cities remaining to visit

I managed to see a great many of the top European cities during my relatively short sojourn there (2005-7).  I think I will list the cities that I would like to see in potential linked-up tours, but then I will simply mark with an x if this would actually be a return visit.  I think we're still a minimum of 3 years away before I would consider taking the kids, since my idea of a vacation to these places is mostly to take in the cultural sites, and that simply won't work if they 1) don't have the stamina or 2) are completely resistant to the idea of spending so many hours in museums.  I can tell that Madrid, Vienna, Berlin and Munich would all be major challenges.  Paris, Amsterdam and Prague have more attractions to compensate for the museums, but that does assume we could schedule a day off from museum-going...

These aren't precisely ranked, but just trips that I would like to take before I get too old to enjoy them.

Paris(x) - London(x) - Oxford - Cambridge(x)
(The trip we would probably make first.)

Germany: Munich - Frankfurt - Cologne - Berlin(x) - Leipzig? - Dresden??

Italy: Rome(x) - Florence - Venice - Milan?

Spain: Madrid(x) - Barcelona

Amsterdam(x) - Rotterdam?

Prague(x)

Brussels ?

Geneva ? - Zurich ?

Vienna(x) ??

Stockholm ??

Russia: St. Petersburg - Moscow
(As mentioned before, this is very low on the list, but never say never.)

Cairo
(As much as I would love to see the Pyramids, I don't foresee a stable situation in Egypt anytime soon.)

Mexico City ?
(To see the great murals, particularly by Diego Rivera)

Beijing ?? - Shanghai ?? - Hong Kong ??
(Most likely I would only go in conjunction with work, just as I doubt I would visit Australia if there wasn't a work connection.)