I didn't master my first CD, but I did with my second, and it was so worth it. In my case the mastering engineer, Charlie Pilzer of Airshow (also one of the very best), also did most of the mixing - and played bass! He's a joy to work with.

Kara asked about panning and eq. Yes, that's mainly done in the mixing process. In the mastering process the work is done with just two tracks - left and right - so that any eq added affects a whole song (or indeed the whole album). In mastering the engineer will help you create a CD which is enjoyable in different environments (ie, the car, your house, the radio, an i-pod), and eliminate extraneous pops and noises. If there are significant mistakes in the mixing, the mastering engineer should be able to catch them so the mixing engineer can fix them. (You'd be amazed at how often this happens). In the end, you'll have a recording that people want to listen to, not only because of your performance, but because there's nothing in the audio which is subtly discouraging them.

With the right mastering engineer, your CD should end up sounding more like you than you do! Will it be completely natural? No, but we gave that up the moment we took the human voice and instruments and put them into a recorded medium broadcast into a room with two pieces, to be listened to while people do the dishes or drive home from work. What it will do is present you in the best possible way to the world.

So yes, I'd be a vote in favor of mastering - your CD will represent you forever, so it's worth the investment to do it right. What I would NOT do is have a folk CD mastered (or recorded or mixed, for that matter) by someone who doesn't understand and love folk music. You need someone who can understand what you want, who will listen to you and also talk to you clearly.

Good luck with the project, CB!

Dan