Worth it carrying spare spokes?
It's pretty easy/light to carry around a couple extra spokes per wheel and a pretty good idea for a long tour.  You'll probably need a few different lengths though for the front, rear left, and rear right sides. 

Another good option is to carry an emergency fiberfix spoke that can be used with most wheels, which will help in an emergency.

http://www.amazon.com/FiberFix-Emergency-Spoke-Replacement-Kit/dp/B001GSMQZC

You may want to work on your skills with truing a wheel without a stand as well. You can use a couple zip ties on your seat stays in place of a truing stand. Just make sure you are comfortable with this process before you go on the road, and don't forget your spoke wrench.  You may need a cassette tool / chain whip as well if you need to replace a spoke on that side of the rear wheel.