Do refreshments attract audience to seminars?
I think you should approach the question slightly differently - don't ask whether more people will come to your presentation because there are refreshments. Instead, ask whether refreshments will enhance the overall experience. In my experience, refreshments help to keep the group together after the event is over, which in turn allows for people to mingle, share ideas, and get to know one another better. When refreshments aren't provided, people tend to bolt out the door immediately following the end of the lecture. In this sense, refreshments give you the chance to build community, and give undergrads, graduate students, and junior scholars the chance to bend the ear of a senior scholar.