I liked how we did it my freshmen year. (Alas, I have missed the past two Founder's Days because we always have it on the weekend of my birthday.)
We rented out a nice reception hall on campus and decorated it with balloons. An alum made these really cute angel centerpieces, which for a very low price you could buy following the banquet. (I still have mine!) We served finger food and mingled with actives and alum. Next, we honored the seniors. That year we made a slide show will all of the seniors, and then the alum club president made a small speech about Pi Phi and "inducted" the seniors into her club.
It's simple but not dreary. Maybe you could choose a few alums to read a small blurb on why they joined Pi Phi? Or talk about some of their collegiate experiences? Just some ideas....
PPL,
Erin