What? He's used to running for his life, so that wouldn't faze him, he's used to big ugly scary evil monsters, so megalomaniacs would be a piffle, and he's the ultimate traveler.
In fact, Twoflower would probably have a blast traveling with the Doctor, too. Think of all the pictures he could take!
While I'm on the subject of crossovers, I've been having this plot bunny plague me for at least a week. It's a crossover between Doctor Who and the Thursday Next series by Jasper Fforde. This is the bunny: the alternate universe Rose got stranded in--Pete's World--is actually the universe of Thursday Next. Sometime between the timeframe of the books (which I believe is mid-'80s) and "Rise of the Cybermen", the Goliath Corporation merged with Cybus Industries. Now that Cybus has shut down, Vitex is taking over as the new corporate overlords (but they're benevolent overlords). Thursday has been promoted from SO-27 to SO-2, Weirder Stuff, which is actually Torchwood. After the Cyber Wars, Thursday becomes head of Torchwood, and that's when she meets Rose. They have adventures, they complain about paperwork, yadda yadda yadda.
The only problem is--well, I haven't read all of the books. But I have this whole crossover universe in my head! And think of all the problems Rose would have with history and science--she'd have to go back to school all over again. Most fic writers don't deal with that issue--since zeppelins are all over Alt!London, the Hindenburg crash probably never happened. What other historical events never happened in Pete's World?
Also--and this is the great part--in this crossover, time-travel is possible. (SO-12, the ChronoGuard.) Who's up for a little Captain Jack? Methinks he and Thursday's dad are pretty good friends. *grin*