Yes, the Candlelight Processional is definitely worth it. My wife and I have seen it every year for quite some time now and it's become part of our holiday tradition. It's very inspirational and will fill you with Christmas spirit.
The Processional is very, very popular and if you really want to see it, I would recommend one of the dinner packages. The America's Garden Theatre fills up very quickly. You could always stand outside the theater and listen, but it's just not the same.
Here's a link to more
Candlelight Processional information as well as last year's various dinner package options. You won't regret booking a dinner package!