" "The attention span seems to have grown pretty short."
This isn't incorrect, but it's somewhat misleading. I hold people's attention no problem - and my style is not flashy in the slightest. I'm a story teller, I intrigue them with a narrative that they take part of. I don't think that attention spans have gotten all that short - I think that what it takes to hook the attention has changed. In that sense, the performer has to prove immediately that they are worth the audience's time and attention. Because the audience has spent all day, every day, barraged by BS that isn't worth their time.
Contemporary audiences have developed an extremely effective BS filter (Due to advertising and the abundance of entertainment available). You have to prove you're not BS."
This extract from a post by Christopher T on another thread might help you somewhat. I've noticed that many people are genuinely curious about magic and just having cards in my hand practicing one thing or another I've been asked if I can do a trick. So I think the problem is less to get passers-by to stay and watch for a few seconds, but to hook them in these few seconds. And this is important: Assuming you were going about your business in town and saw a performer yourself. If you didn't see something interesting in the first few seconds, would you wait around a few minutes until something spectacular happens (if something spectacular happens), or would you get along with your business? On the other hand, if something fantastic happens immediately, you'd probably wait around for the next great thing to happens.
So, the biggest challenge is grabbing the attention of any passers-by.
Hope this helps a little bit!