Any advice or tips on the Civil Affairs Selection Course? I'm strongly considering attending.

Teamwork.
Everyone has a job, not just the person engaging. Designate personnel for security, observing the non-principals, and spot engaging secondary officials.
The Q-course is heavy on misdirections. If your conversation takes a turn to the surreal, such as weird outbursts or people becoming emotional for no real reason, stuff is about to go South.

Make sure you secure your information requirements and resist efforts to suck you into unrelated topics. Employ your own misdirection to confuse the role players on what information you are after.

Find out who has experience in what on your team and USE IT.

This is not a job for wallflowers or followers. Don't be one.

You need to be physically prepared for a challenging course. The physical piece doesn't drop too many enrolled students, but it comes as a rude awakening if you expect a gentlemen's course.

All I'll say is be physically fit and have an open mind. Be social in your team because that plays a crucial role; don't be that reclusive, weird dude that nobody likes because that will get you nowhere in the CA branch. I won't tell you anything about CAAS because it's meant to put you out of your element. Even if I wanted to, I went in 2012 and I'm sure it's completely different now.
If you decide to go, good luck!

It changes all the time, prepare physically and be yourself. The cadre are assessing for the right people, not someone who is going to put on a facade to get selected. If you are the right person you'll get selected, if not, thanks but no thanks. Like it has been said, you will be required to talk to people and gather information, and you will work in a team. Don't mean to sound cryptic or like an ass but the point of CAAS, like SFAS and POAS, is to pick the right person, not just be a way out of a different MOS.