So what exactly is "interesting" to the average person? Is there any single event that consistently engages even 15% of the local population? I don't really have much personal interest (or the time) to attend 95% of the events around GR, but I'm happy people turn out for them and make an impact on someone's economy.
Lots of people do not enjoy The Griffins/Rampage/Whitecaps/Kenny Chesney/tractor pulls/symphony/opera/Broadway Theater Guild...but few question the contributions these events make to our community. And what about The John Ball Park Zoo, Frederik Meijer Gardens, GRAM? Lots of locals never darken those doors...but most would agree they are invaluable to the fabric of GR and create a positive impression of GR that far exceeds the numbers at the turn-styles.
SXSW is a predominantly a music festival so your comment about people not "coming out to see the art" in Austin is a little misleading. ArtPrize will include all art, and that can include music, film, digital projection and all forms of traditional media. So if you don't like a particular piece of art/media you can always stroll down to the next building hosting an entirely different artist.
If 300,000-500,000 people turnout annually for our proud (but very tired) "Festival of the Arts" every June to eat questionable food for 3 days, ArtPrize's potential to draw a significantly larger and more diverse audience over a 2 week period is incalculable at this point. The bottom line is you're going to see an international art competition with 1000's of visitors coming to GR from this country and many others.
Giddy up.