I've been three times to the CP (once with the dinner package but back then it was a lot cheaper and included tip). First time (2001) we waited in a really long line but made it in. I can't remember who was the speaker but it was good (I think it was boring for most of the kids around me as most were asleep or not paying attention). The next time (2005) we did the dinner package but got out of dinner later than expected and they had already started letting the general public in. We still got pretty decent seats. Then (2006) we waited maybe 15 minutes in line and still had good seats (of course it started to rain/sprinkle a little bit through it so that may be why the line wasn't extremely long). We've always gone in the middle of the week and the second week of December.
The dinner package may be becoming more of a necessity though as I've heard (but don't know how true this is) that they've been releasing more tables for the packages every year and they also just started a holiday tour ($179 pp) that includes seats at the CP (making less seats available for walk ups).
I think everyone should do it once (although I can't say it's worth the cost or the sacrificing of 2 credits to go if you go the CP package route). I think in the future I may just stand at the back of the theater and watch a few songs and then continue enjoying World Showcase (45+ minutes on a metal bench is not comfortable). The singing is always so good and the speakers are usually well spoken (nothing in particular was memorable about any performance; they get up, read a section of the story, sit down, the choir sings, they get up read another section, etc.). It is very festive and will get you in the Christmas spirit. If you do go be sure to bring a sweater or something to sit on as the metal gets cold quick in the evening (and maybe a poncho in case it starts sprinkling/raining).