I can attest for both good and unpleasant (but never really threatening) scenarios during my travels, perhaps illustrating very well which places one should expect trouble the most. For examples, one time while waiting for my ride near Milano Centrale I was accosted by some nasty looking individual who asked for a cigarette, made it look like he accidentally dropped it, then asked for another.. asking for trouble basically. While at other time, in central Mexico getting lost while riding, I simply talked in my spanglish with a cab driver who agreed for me to follow him until my destination address, but then to my surprise did not accept any money in return. Vaya con Dios!
I think it really depends if one is open minded and likes to enjoy the travel experience, while for others the simple idea of leaving their home town and familiar places seems lunacy.
Finances, accouterments and comfort & accommodations is where it really becomes very different for everyone. I have met people who would absolutely not sleep in a tent or go in a place without regular bedroom and bath. And I have not yet met anyone who enjoys gas station food ;-)