Total 60s homage
I'm surprised no-one has remarked on this: "The Tourist" is clearly an homage - verging on an ouright spoof - of what amounted to a 1960s genre, namely the romantic comedy/thriller romp.
Think Hitchcock's "North by Northwest" (which has a very similar plot - hapless sap meets mystery woman on train and gets embroiled in a mistaken identity chase). Think "The Italian Job". Think various Bond movies.
Sure, it has a groan-inducing denouement. Sure, it has corny acting and bad guys who can't shoot straight. A heavy who should be stroking a white Persian cat. Boat chases through Venice. Cliches all, and that's the whole point.
It's no masterpiece for sure, but I'll bet they had great fun making it, and I had fun watching it.