I've been!
Personally I thought it was great...better than the Christmas ticketed event that is also very popular. A wonderful, fun, party atmosphere, so yes, IMO it was worth the money - I wouldn't hesitate to go again if I was there at that time of year.
Crowded...ummmm, depends what you are comparing it to - I hear ticket sales are limited to the region of 30,000 which is about the same as a reasonable off-season day. In other words, there will probably be waits of 20-30 minutes on the rides at peak times....however, if you (and if you've kids) have the stamina to stay till the end, then crowds fall off quickly after the fireworks, so what we do is ride the rides we want during the first parade, wander around until after the fireworks, see the 2nd parade, and then maybe walk on a ride or two just before park closing...it worked for us.
We didn't wear a costume and didn't feel out of place, however if I went again, I'd probably make an effort...just because it was obvious that people who did dress up were having so much fun!
Any other questions, fire away
Penny