Welcome to GC!
We don't do themes, per se, at my school, but for our formal recruitment this year, our theme for Skit Day is "Wizard of Oz". I think that this would make a gret theme for panhel in general... You could do a lot with the saying "there's no place like home".
As for different days, the one thing we seem to do differently at my school for recruitment is called formal desserts. Open houses and skit day are the first two days of recruitment, and they are both open days (and required). The first invite round is formal desserts, in which the PNMs have dessert at each house they were invited back to/selected to go back to. There's only three houses, so it's managable... I can see this being a problem if you had to eat dessert at ten houses!
Anyway, it's a nice way to be able to sit down and chat with one or two of the PNMs before pref parties, which are the next day.