Glad to hear you're interested in joining! I'm a Cadet Lieutenant Colonel and I owe most of what I've learned about leadership so far to CAP.
Since I don't know this squadron, there's certainly no harm in dressing nicely. Anywhere from a polo shirt and jeans to shirt and tie would definitely make a good impression if I was meeting you as a prospective cadet.
Be comfortable in the clothes you're wearing, ask questions, and have fun! I'm always available to answer your CAP questions as well.