Aria,
Definately send them out. As far as the thank you cards go, it's just a gesture of thanks for the adcom who took the time out of their busy schedule to sit and chat a bit. It just shows your maturity level and appreciation for the opportunity to interview at the school (considering the fact that many schools only interview like 7% of applicants). I like to keep mine short and sweet, like a few sentences that say you enjoyed going over your application and look forward to hearing from the admissions committee soon. If you can remember any specifics about the interviewers interests or something that makes you stand out then mention it with a P.S. at the end. Hope this helps...good luck with all of your interviews! Ciao.