I have taken a night train out of Prague to Basel and we absolutely loved it (I know it's not for everyone) and we will likely do it again this coming spring. I am also looking at doing one between Venice and Prague.
From what I can now (it would be in the spring) it looks like they have couchette sleepers but nothing deluxe (so no private wc) which is fine but something to think about. It also seems like it may cost a lot more and we'd waste a lot of time getting back to the Venice Airport and transportation from Prague Airport into town.
I would love to hear thoughts on Venice to Prague and whether flying or the night train is better or more cost effective, etc.