Some schools require at least a year of college cheer. I can tell you that the skills you learn in all-stars will absolutely help you, but at tryouts you will likely be up against all-star kids with gameday skills from high school. It is not unusual for kids with amazing skill to be passed over for kids with cleaner, easier skills because they have good gameday skills. Remember that colleges don't care about cheerleaders competing, but rather about us performing well at games. Bad gameday performance can result in the elimination of a school's cheerleading program. You should know how to spirit with and without poms, yell (even while stunting) and use signs, poms and megaphones. Here are some videos that should give you a better idea of what gameday skills should look like:
Skip to 1:00
(Notice the sharpness of the motions and the facials; some are a bit overdone, but you get the idea)
Skip to 1:24 (band dance), 1:58, 2:57, 4:00, 4:25
(notice how they spirit)
Skip to 1:20, 2:50, 3:23 (band dance and great spiriting)
I recommend watching the whole thing.
Edit:
@ACEDAD I'm sure you can guess why I'm tagging you.