Whilst travelling by train is rather nice, have you considered flight? The budget airlines are insanely cheap over there (when I got the first quote for the flight, LON-VEN flight, booked online, cost roughly 30 Euros through EasyJet.) Just FYI :)

Sadly we won't be going to Venice on this trip, but we're still going to Carnivale at some point (read: priority for next Euro trip).