I have to admit that lately I've been building very little railroad lines in my games. I know that they are useful when it comes to troop movements and such, but by the time I have railroad I find that I am usually ahead and I'll only build them in places like mined hills and buffalo squares to get the shield bonus. My cities can usually defend themselves well by this time, and my biggest threat usually is barbarians popping up.
If I have a rival on the same continent as mine, I am usually more interested in taking them over instead of trading. Also, I tend to trade with cities (my own or others) on different continents in an effort to get a bigger bonus. What can be nice is to put a single city near a rival's main civilization (or take over a city) and bring lots of caravans and freight there and use the other civ's rail lines to disperse your trade at various intervals.
I have my settlers and engineers settle cities when they can, build roads for trade, and develop irrigation for growth as a priority. Then would come mining and the irrigation of things like swamp and jungle before railroad lines in many cases. I am probably in the minority when it comes to my sparse use of rail, but it's just my personal preference lately.
------------------
Diplomacy - the art of
saying "Good Doggie"
until you can find a rock