*waves* YAY another guardie. haha
I was in colorguard in high school, and we went to WDW with band my frosh and senior years, and let me tell you, they were SOOOO much fun.
We marched before the Share a Dream Come True parade in MK both times. It's an awesome feeling to be marching down Main St with sooo many people watching you. It especially was cool my senior year, as I was co-captain and along with my other co-captain, we were leading the flagline, so it was such a rush.
Plus, you get to do the Magic Music Days workshops. The band normally does one where they learn music to one of the disney movies, play it, record it, and then have it meshed together with the movie, so instead of the original score, it's them playing in the background.
The guard does a dance workshop. They set it up as a mock-audition dance thing, and it's really fun. They teach you the choreography from bits of some of the shows from WDW, and then we perform them.

My guard does Winter Guard, so we also got to perform our own winter guard routines at the Tomorrowland Stage in MK, which was also amazing.
One of the coolest parts is seeing the backstage part of disney. and also, if you've never been to WDW without parents, it's SO much fun. We got to roam around with a minimum of 3 students (by ourselves, no chaperones), but had to check in ever so often. Normally, check ins were around noon and 6, so we could get the money/meal tickets for lunch and dinner.
Have fun and if you have any more questions, feel free to either PM me or write them in this thread!