Epoxying the spars is sort of like belts and suspenders.  It won't hurt, it takes a bit more time & materials, but not strictly necessary.  Hopefully, your spars won't spend an appreciable amount of time in the water...;^)

I've noticed that my spars get a bit more dinged up since they're just varnished, so if you're going for a museum piece look, you might want to epoxy them to harden them up a bit.

 I took the easy way out on my Skerry, based on advice I saw somewhere in the manual, (or maybe it was the NE Dory manual or a sail kit addendum) and skipped the epoxy on both the spars and the mast.  This is my third summer, and I've had no problem at all with the spars, but the varnish near the bottom of the mast takes a beating, and I found after a particularly wet sail one day that the bottom of the mast had actually swelled up enough to make it difficult to unstep.  I would advise epoxy on the mast, optional on the spare.

hokker 

Hokker makes a great point, although I would think the rocker would drain the mast step quickly.

My other thought was that there are numerous times during the boat building process when you might have a bit of unused, unthickened epoxy and are wondering what to do with it.  Epoxying the spars is a perfect use for that.  

When I did my build, I tried to have an overall understanding of the build process, big-picture style, and not just follow the manual step by step.  This enabled me to approach my build from a parallel solution instead of a series solution, so I was making spars and tiller/rudder parts, daggerboard, etc. while waiting on a particular step in the boat build to cure.

I have a similar approach to yours with projects CaptainSkully. I've found that not only does it make the project progress more smoothly but also usually leads me to gain new understanding in areas I've not explored before.