I have no idea how much it costs to register, $10 or $1000, but since it sounds like it's not too much...
What about the prestige factor?
You're proud of your dog obviously (who isn't?) and you probably want other people to appreciate your dog as much as you do. Since they always ask (at least they ask me) if Lady has a pedigree, it's nice to be able to say yes. That shuts up all the snobby dog people who judge a dog on background only, and is important for nondog people to hear (i.e., you could tell them a pedigree is ONE of the tools used for evaluating the quality and responsibility of the breeder's program).
As an aside, I agree with Cubby, posting combat stresses me out.
I will be interested to hear what you decide - we were in a similar position and decided to register Lady since we weren't sure if we wanted to show her, and I am glad we did. -Mariah.