Originally Posted by Koby

I second the suggestion of leaving out Rotterdam unless you have a good reason to go there. And the same goes for Bonn.

And unless you have added Vaduz to your list because you wanted an extra country on your list, I would just continue the trip from Zurich down to Italy. But by all means, do spend time in Switzerland somewhere between Zurich and Italy. Luzern is a good suggestion.
And I'm a big fan of taking the train through Switzerland towards Italy. But please don't take a night train! Travel during the day and enjoy the views.

Also, at the beginning, instead of going directly from Amsterdam/Rotterdam to Brussels, you could stop in Antwerp(en). You can then spend a few hours there before taking a train directly towards Gent and/or Brugge (and go to Brussels after that).
(Disclaimer: I say "could", because I used to live in Antwerpen and am therefore not 100% neutral. But I do think that if you are in the area it would be a shame not to spend at least a few hours there and visit the main square and the cathedral.)