I started off with waterproof working boots and ended up ditching those... Honestly, I think a good pair of sneakers will do.
When it comes to the kind of traveling I do / plan to do (urban areas, coach/passenger train/hitchhiking) I second that. I often have issues with my shoes, cause I prefer lightweight canvas shoes (chucks, vans) and I wear them out quite quickly (esp while traveling). But I get along with it and don't care if they are ripped or whatever as long as they are comfortable. Only shoes that gave me blisters recently were new shoes.
Now, I wear a pair of hiking sandals since it's the summer, even manage to hop trains with them. It really all depends on what works for you (personal preference/personal experience).
Yes, it depends on circumstance, IMHO. To be honest, I wouldn't ride freight wearing sandals. In that case I would wear sturdy boots. (Riding freight is out of the option here anyway, so I don't care about that.) But if it works for you, why not?
I see it this way: if my shoes fall apart, I can fix them with tape and get replacement everywhere for cheap. I always have flip flops in my backpack as emergency shoes (or just to wear in a hostel or for a walk downtown). On the other hand, would I plan to hike far away from civilization I would definitely care more about robust, comfortable shoes, cause I would depend on them and the ability to walk long distances. So, as you wrote, it depends.
Just my 2 cents ...