As a highschool student, I will have to honestly admit I didn't know ANYTHING about these conferences until I went to nationals with my team, and that's only when I saw signs. I would recommend getting a memo out to teams about this opportunity and giving people a better idea about what options they have.
I really like all these ideas. I think conferences either on the day before practice or the day of would be nice for me because that's when our team usually goes down anyway, but remember that it can be difficult for college/highschool students to get out of that much of classes (loss of credit, projects, etc.). Something that may be effective is programs after the playing day, or maybe doing lunch programs where individuals can go to purchase lunch and attend a talk. Though you might get people who are just interested in the food, they will become interested in the conference if you make it fascinating and fun. Food is always always always effective.
As far as programs go, I would imagine you should throw in a bit of everything. What about medicine? I know many friends in robotics who are only doing engineering for undergrad. Info on how this applies to med school would be fantastic. Also, this is a good time to make contacts. Do presentations that involve the students doing things. Give them opportunities to go see the championship competitions during the day, but give them something to come back to and be interested in. Word of mouth spreads, and if this year's group enjoy it, they spread it around cause they want their friends to come.
Good luck! I definitly plan to attend if my team doesn't make nationals.